Radical Site Research Articles

PAH growth assisted by five-membered ring: pyrene formation from acenaphthylene

To investigate the role of five-membered rings in the growth of polycyclic aromatic hydrocarbons (PAHs) in flames, the conversion of acenaphthylene to pyrene with substituted phenalene as intermediate is studied through quantum calculations using CBS-QB3 composite method. Two pathways are considered, where one initiates with H-abstraction from the five membered ring on acenaphthylene, while the other initiates with H-addition on it. Both the pathways are then followed by subsequent C2H2 addition reactions on the radical sites. With the first C2H2 addition, a substituted phenalene-type species is formed, which undergoes another C2H2 addition reaction to lead to pyrene formation. The reaction kinetics are calculated using transition state theory, and the new reactions are added to a detailed hydrocarbon mechanism to test their effect on the profiles of pyrene and other PAHs. Among the H-abstraction-C2H2-addition (HACA)-type mechanisms for pyrene formation, the proposed reactions have a minor contribution in pyrene formation as they mainly form 1-ethynyl-acenaphthylene and phenanthrene. Through mechanism analysis, the reactions primarily responsible for pyrene formation are highlighted that require further investigation.

An assessment of soot chemical property from a modern diesel engine fueled with dimethyl carbonate-diesel blends

Dimethyl carbonate (DMC) is a promising alternative fuel for diesel engines. Comparing with the traditional diesel fuel, the DMC application can lead to a different combustion process where the soot is synthesized, yielding variation in chemistry of engine-out soot particles. Soot chemistry is highly related to the concentration and accessibility of radical sites for the reactions regarding to soot oxidation on the exhaust systems or during DPF regeneration. Therefore, the study on the chemical feature of soot emissions is of great necessity. Nevertheless, comprehensive determination on the soot chemical property for DMC-contained fuel and its instinctive explanation is not well understood in the previous studies. In this study, to reveal the effect of DMC addition on the chemical feature of soot emissions, the surface functional groups and their bonding states of soot particles from various DMC-diesel blends were characterized using FT-IR and XPS technologies. Results showed that the DMC addition exerts different influences on the surface oxygen content, oxygenated groups and their bonding states with various DMC content. Therein, DMC addition in large amount can significantly increase the C sp3/sp2 ratio and the concentration of C-O epoxies on soot surfaces. At relatively low engine speed and load conditions, the low-content addition of DMC leads to slight increase in the aromatic C–H/aromatic CC ratio in soot bulk structure. However, the large-content DMC addition distinctly reduces the aromatic C–H/aromatic CC and aliphatic C–H/aromatic CC ratios. The results are useful for the prediction of the subsequent soot oxidation behavior during DPF regeneration on diesel engines.

‘A Show Opened to All Artists’: The 1970 Liberated Venice Biennale and the Production of Dissent

In 1970, a group of New York City artists sought to ‘liberate’ the world’s largest art exhibition – the Venice Biennale – reimagining it as a radical site for political dissent. Their target, the United States of America’s pavilion, had promised more than just an exhibition, claiming that its show of print works, accompanied by an active workshop, would provide ‘a non-political setting for direct exchange among people who share the common interest of drawing the international community into harmony’.1 Instead, before the Biennale even began, over half the exhibition’s original thirty-three artists withdrew, emptying out the pavilion and throwing government plans into disarray. This was an act of protest, a boycott by artists against the instrumentalisation of their work by a government embroiled in a brutal war in Vietnam and facing anti-war, civil rights, and student protests in the USA. For the boycott organisers, withdrawal was a political...

High-Pressure-Limit and Pressure-Dependent Rate Rules for Unimolecular Reactions Related to Hydroperoxy Alkyl Radicals in Normal-Alkyl Cyclohexane Combustion. 2. Cyclization Reaction Class.

The hydroperoxy alkyl radicals are important intermediates in the low-temperature combustion for normal-alkyl cycloalkanes, and the cyclization reactions of hydroperoxy alkyl radicals to form cyclic ethers are responsible for a major fraction of the OH formation, which has the potential to promote ignition. In most of the previous modeling studies for normal-alkyl cycloalkane combustion, the kinetic data of the cyclization reactions in the detailed combustion mechanism were mainly taken from the analogous reactions in cyclohexane, methyl cyclohexane, and alkanes in published literature studies. In this work, the kinetics of the cyclization reaction class of hydroperoxy alkyl radicals in normal-alkyl cycloalkanes is studied, where the reaction class is divided into subclasses depending upon the ring size of the transition states, the types of the carbons on which the -OOH site is located and the types of the carbons on which the radical site is located, and the positions of the cyclization (on the alkyl side chain, on the cycle, or between the alkyl side chain and the cycle). Energy barriers and high-pressure-limit site rate constants and pressure-dependent rates for reactions in all subclasses are calculated, and rate rules for all subclasses are developed. The high-pressure-limit rate constants are determined from CBS-QB3 electronic structure calculations combined with canonical transition-state theory calculations, and pressure-dependent rate constants are calculated by using the Rice-Ramsberger-Kassel-Marcus/Master Equation theory at pressures varying from 0.01 to 100 atm. Comparisons of the rate constants for cyclization reactions of hydroperoxy alkyl cyclohexylperoxy radicals calculated in this work with the values of the corresponding reactions in some of the popular combustion mechanisms show that it is unreasonable to use the kinetic data of analogous reactions in alkanes, cyclohexanes, or smaller normal-alkyl cyclohexanes. Therefore, the accurate kinetic calculations and the construction of rate rules for normal-alkyl cycloalkanes are necessary and significant for the reliable modeling of the low-temperature combustion of normal-alkyl cyclohexanes.

Growth of Polycyclic Aromatic Hydrocarbons by C2H2 Mediated by Five-membered Rings: Acenaphthylene Conversion to Phenanthrene

ABSTRACT To investigate the role of five-membered rings in the growth of PAHs, the conversion of acenaphthylene to phenanthrene is studied using density functional theory and composite method. Two pathways are considered that initiate with H-abstraction from different sites on acenaphthylene and are followed by acetylene addition on the radical sites. The reactions in both pathways progress with the formation of two fused five-membered rings and H-migration reactions that eventually get converted to a six-membered ring to form either phenanthrene or phenanthryl radical. The reaction kinetics are calculated using RRKM theory, and the new reactions are added to a detailed hydrocarbon mechanism to test their effect on the profiles of phenanthrene and acenaphthylene. The flame simulations indicate that the phenanthrene concentration increases by 58% with the addition of the proposed reactions to the mechanism and helps in matching the experimental phenanthrene profile with the computed one. Thus, the pathways studied in this work can be considered to be important for phenanthrene formation.

Continuous Butadiyne Addition to Propargyl: A Radical-Efficient Pathway for Polycyclic Aromatic Hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) play a crucial role in soot inception, interstellar evolution, and nanomaterial synthesis. Although several mechanisms, such as hydrogen-abstraction acetylene/vinylacetylene addition, have previously been proposed, PAH formation and growth are not yet fully understood. We propose an alternate PAH growth mechanism wherein propargyl radical reacts with butadiyne to form larger radicals containing newly fused aromatic rings. Butadiyne is an important intermediate in hydrocarbon oxidation and carbon rich stars, while propargyl is one of the most important resonantly stabilized radicals that persists for long times. Our proposed mechanism is validated by quantum chemical calculations, elementary reaction experiments, laminar flame analysis, and kinetic modeling. Our findings challenge the conventional wisdom that radical site regeneration, being central to PAH growth, requires sequential hydrogen elimination and/or abstraction. In our proposed mechanism, PAH growth does not depend on abundant free radical consumption, and could, therefore, help explain carbonaceous nanoparticle coalescence in radical-deficient reaction environments.

Extra Sodiation Sites in Hard Carbon for High Performance Sodium Ion Batteries.

Hard carbons are promising anodes for sodium-ion batteries (SIBs). However, the low practical capacity from limited sodiation sites impedes their applications. Herein, ultrahigh concentration of pyridine N (≈7.9%) is introduced inside hard carbon, considering that pyridine N may provide extra sodium storage sites with stable CN• and CC• radicals during cycling. To expose more radical sites for sodium storage, a 3D structure with a multistage pore structure is constructed through NH3 release during the pyrolyzation process. As expected, the hard carbon with extra sodiation sites exhibits an impressively high capacity of 434 mA h g-1 at 20 mA g-1 , superior rate performance of 238 mA h g-1 at a current density of 5 A g-1 and a high-capacity retention of 98.7% after 5000 cycles. The radicals induced Na-adsorption mechanism was further explored through ex situ electron paramagnetic resonance technology, in situ Raman technology and density functional theory calculations. The results reveal that the extra sodiation sites come from the electrostatic interaction at low potentials. This work constructs a sodium ions storage model of extra radicals and provides an extended strategy to improve the electrochemical performance of SIBs anode materials.

Can ‘Territoriality’ be Social? Interrogating the ‘Political’ of Dalit Social Inclusion in India

Social exclusion of Dalits in India is often understood in terms of discriminatory social structures embedded in oppressive cultural domains of pure versus polluted. Territorial demarcation of Dalits from upper/dominant castes is yet another way of perpetuating and sustaining social exclusion while segregating them in separate neighbourhoods built on the Varna principle of graded social inequality. However, over the last few years, Dalits have gathered some strength to say no to social exclusion while re-territorializing their segregated living spaces into radical sites of social contestation. Dalit counterculture and alternative Dalit heritage are what provided the necessary material for the re-territorialization of Dalit segregated neighbourhoods. The central concern of this study is to unravel what led to transformation of separate Dalit neighbourhoods into social territoriality of contestation.

Development of a Detailed Kinetic Model for the Oxidation of n-Butane in the Liquid Phase.

The chemistry underlying liquid-phase oxidation of organic compounds, the main cause of their aging, is characterized by a free-radical chain reaction mechanism. The rigorous simulation of these phenomena requires the use of detailed kinetic models that contain thousands of species and reactions. The development of such models for the liquid phase remains a challenge as solvent-dependent thermokinetic parameters have to be provided for all the species and reactions of the model. Therefore, accurate and high-throughput methods to generate these data are required. In this work, we propose new methods to generate these data, and we apply them for the development of a detailed chemical kinetic model for n-butane autoxidation, which is then validated against literature data. Our approach for model development is based on the work of Jalan et al. [J. Phys. Chem. B 2013, 117, 2955-2970] who used Gibbs free energies of solvation [ΔsolvG(T)] to correct the data of the gas-phase kinetic model. In our approach, an equation of state (EoS) is used to compute ΔsolvG as a function of temperature for all the chemical species in the mechanism. Currently, ΔsolvG(T) of free radicals cannot be computed with an EoS and it was calculated for their parent molecule (H-atom added on the radical site). Theoretical calculations with the implicit solvent model were performed to quantify the impact of this assumption and showed that it is acceptable for radicals in n-butane and probably in all n-alkanes. New rate rules were proposed for the most important reactions of the model, based on theoretical calculations and the literature data. The developed detailed kinetic model for n-butane autoxidation is the first proposed model in the literature and was validated against the experimental data from the literature. Simulations showed that the main autoxidation products, sec-butyl hydroperoxides and 2-butanol, are produced from H-abstractions from n-butane by sec-C4H9OO radicals and the C4H9OO + C4H9OO reaction, respectively. The uncertainty of the product ratio ("butanone + 2-butanol"/"2-butoxy + 2-butoxy") of the latter reaction remains high in the literature, and our simulations suggest a 1:1 ratio in n-butane solvent.

Magnetic Modulation in Heteroallene and Heterocumulene Based tert‐butyl Nitroxide Diradicals: Spin Delocalization and Conformation Play Crucial Roles

We have theoretically investigated the magnetic properties of heteroallene (>C=C=X-) and heterocumulene (>C=C=C=X-) based tert-butyl nitroxide diradicals (X is P/As). Calculation of magnetic exchange coupling constant (J) shows ferromagnetic interaction in heteroallene based diradicals. Whereas, in heterocumulene based diradicals, tuning of J value from antiferro- to ferro-magnetic state is observed from Z- to E- isomer. Delocalization of spin density from radical site to the coupler (in planar arrangement) is observed in spin distribution analysis which is also advocated by molecular orbital analysis. The typical feature of tert-butyl nitroxide radical creates spin delocalization along with spin polarization within the coupler. The J values of all the diradicals strongly depend on the dihedral angle between radical center and coupler. Magneto-structural correlation shows that the change in dihedral angle tunes the magnetic property for both the Z- and E- isomers of heterocumulenes depending on the spin accumulation on two nearby magnetic centers. The extent of spin delocalization and conformation of spin centers on the molecular axis are important for the different J values observed in our designed systems.

Reactivity of para-benzynes in solution and in the gas phase

To rationally design less cytotoxic synthetic drugs based on biologically active para-benzyne intermediates, it is essential to obtain a better understanding on the reactivity of para-benzynes. However, little is still known about their fundamental chemical properties, which requires examination of pure species in simple solvents instead of biological matrices. While fundamental solution studies are limited, the solvent-free reactivity of protonated para-benzynes has been examined previously in the gas phase by using mass spectrometry. In order to facilitate the comparison of results obtained in the gas phase and in solution, we attempted to compare the reactivity of a neutral para-benzyne analog toward dimethyldisulfide in solution to that of its protonated form in the gas phase. The neutral para-benzyne analog, 5,8-didehydroquinoline, was successfully generated via photolysis of an enediyne precursor in dimethyldisulfide/methanol solution and the reaction products were analyzed using a dual linear quadrupole ion trap tandem mass spectrometrometer. However, examination of of the reactions of the same para-benzyne in its protonated form in the gas phase in the mass spectrometer proved to be challenging. Therefore, an analogous, isomeric para-benzyne cation, the 5,8-didehydroisoquinolinium cation, was instead generated in the gas phase from the 5-iodo-8-nitroisoquinoline precursor and its reactions with dimethyldisulfide were examined. This protonated para-benzyne reacted with dimethyl disulfide in the gas phase in the same manner as its neutral isomer in solution; both predominantly abstracted a thiomethyl group by each of the two radical sites. The structures of these products were verified by tandem mass spectrometry experiments based on collision-activated dissociation and using an authentic model compound. These findings suggest that the reactivity of the studied para-benzynes toward dimethyldisulfide is similar in spite of their different protonation states and the different phases in which the reactions were carried out.

Chemical feature of the soot emissions from a diesel engine fueled with methanol-diesel blends

The chemistry of soot particles has high affinity with the concentration and accessibility of potential radical sites for the reactions regarding to soot growth and oxidation behaviors during in-cylinder combustion, and thus affects the particle emissions of the engines. The addition of methanol in diesel fuel is widely believed to transform the soot formation and oxidation behaviors. However, the instinctive explanation on these transformation by soot chemistry is not well understood. In this study, the chemical feature of soot emissions from a methanol-diesel blend fueled diesel engine was characterized, using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), respectively. Results showed that epoxy, ether and C vacancy as well as ester groups were the dominant surface species, while the carboxyl and carbonyl groups exerted less contribution amongst the carbon–oxygen groups on soot surfaces for both of pure diesel fuel and methanol-diesel blends. At low engine load conditions, the increase in methanol blending content led to an increase–decrease-increase behavior of C-O epoxy concentration, which was opposite with the C vacancy contribution. At the higher engine load, increasing methanol content in fuel blends led to higher increment in the hydroxyl species with respect to the epoxy groups on soot surfaces, especially for the 5% and 10% methanol addition. The predominant groups within the bulk of soot particles consisted of aliphatic C–H (methyl and methylene), carbonyl-like CO, aromatic C–H groups and C–O bonds in phenols, anhydrides, esters and ether-like groups for both diesel and methanol blending fuels. Relative to the aromatic CC, the concentration of aliphatic C–H reduced with the increasing methanol content in the fuel blends. The lower-volume-proportion addition of methanol at low engine load led to an increase in the aromatic C–H with respect to aromatic CC. While different, the addition of methanol exerted no significant influence on the aromatic C–H concentration within the soot particles at high engine load condition.

Metastatic testicular and epididymal lesions in a patient with advanced prostate cancer: a case report and literature review

Prostate cancer (PCa) is a second of the most commonly diagnosed carcinoma in the male population. Usually sites of secondary lesions are lymph nodes and bones. Most cases of testicular metastases are incidentally diagnosed after orchiectomy. We present a case of 62-year-old man with metastatic castration-resistant PCa and symptomatic testicular metastasis with contralateral epididymal metastasis. Right site radical orchiectomy and left site orchiectomy was performed. The pathology report identified PCa metastases in the right testis and in the left epididymis. Testicular and epididymal metastases are uncommon in PCa. Therefore, a testicular physical examination is necessary for patients with PCa. Physicians have to keep in mind the possibility of testicular metastasis in cases of biochemical recurrence and progression of the disease.

Protonated Ground-State Singlet meta-Pyridynes React from an Excited Triplet State.

The gaseous 2,6-didehydropyridinium cation and its derivatives transfer a proton to reagents for which the reaction for their singlet ground states is too endothermic to be observed. These reactions occur from the lowest-energy excited triplet states, which has not been observed (or reported) for other meta-benzyne analogues. Quantum chemical calculations indicate that the (excited) triplet states are stronger Brønsted acids than their (ground) singlet states, likely due to unfavorable three-center, four-electron interactions in the singlet-state conjugate bases. The cations have substantially smaller (calculated) singlet-triplet (S-T) splittings (ranging from ca. -11 to -17 kcal mol-1) than other related meta-benzyne analogues (e.g., -23.4 kcal mol-1 for the 3,5-isomer). This is rationalized by the destabilization of the singlet states (relative to the triplet states) by reduced (spatial) overlap of the nonbonding molecular orbitals due to the presence of the nitrogen atom between the radical sites (making the ring more rigid). Both the singlet and triplet states are believed to be generated upon formation of these biradicals via energetic collisions due to their small S-T splittings. It appears that once the triplet states are formed, the rate of proton transfer is faster than the rate of intersystem crossing unless the biradicals contain heavy atoms.

Reactivity Trends in the Gas-Phase Addition of Acetylene to the N-Protonated Aryl Radical Cations of Pyridine, Aniline, and Benzonitrile.

A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N-containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl), and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta, and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios, and reaction efficiencies are measured. The rate coefficients increase from para to ortho positions. The second-order rate coefficients can be sorted into three groups: low, between 1 and 3 × 10-12 cm3 molecule-1 s-1 (3Anl and 4Anl); intermediate, between 5 and 15 × 10-12 cm3 molecule-1 s-1 (2Bzn, 3Bzn, and 4Bzn); and high, between 8 and 31 × 10-11 cm3 molecule-1 s-1 (2Anl, 2Pyr, 3Pyr, and 4Pyr); and 2Anl is the only radical cation with a rate coefficient distinctly different from its isomers. Quantum chemical calculations, using M06-2X-D3(0)/6-31++G(2df,p) geometries and DSD-PBEP86-NL/aug-cc-pVQZ energies, are deployed to rationalize reactivity trends based on the stability of prereactive complexes. The G3X-K method guides the assignment of product ions following adduct formation. The rate coefficient trend can be rationalized by a simple model based on the prereactive complex forward barrier height.

From radical to triradical thin film processes: the Blatter radical derivatives

Thermal evaporation of (poly)radicals is possible. More than one radical site in a molecule makes it more reactive, narrowing the windows left for thin film evaporation, and favouring island formation rather than two-dimensional growth.

Mechanism and kinetics of the oxidation of 1,3-butadien-1-yl (n-C4H5): a theoretical study.

Ab initio CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G(d,p) calculations of the C4H5O2 potential energy surface have been combined with Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations of temperature- and pressure-dependent rate constants and product branching ratios to unravel the mechanism and kinetics of the n-C4H5 + O2 reaction. The results indicate that the reaction is fast, with the total rate constant being in the range of 3.4-5.6 × 10-11 cm3 molecule-1 s-1. The main products include 1-oxo-n-butadienyl + O and acrolein + HCO, with their cumulative yield exceeding 90% at temperatures above 1500 K. Two conformers of 1-oxo-n-butadienyl + O are formed via a simple mechanism of O2 addition to the radical site of n-C4H5 followed by the cleavage of the O-O bond proceeding via a van der Waals C4H5OO complex. Alternatively, the pathways leading to acrolein + HCO involve significant reorganization of the heavy-atom skeleton either via formal migration of one O atom to the opposite end of the molecule or its insertion into the C1-C2 bond. Not counting thermal stabilization of the initial peroxy adducts, which prevails at low temperatures and high pressures, all other products share a minor yield of under 5%. Rate constants for the significant reaction channels have been fitted to modified Arrhenius expressions and are proposed for kinetic modeling of the oxidation of aromatic molecules and 1,3-butadiene. As a secondary reaction, n-C4H5 + O2 can be a source for the formation of acrolein observed experimentally in oxidation of the phenyl radical at low combustion temperatures, whereas another significant (secondary) product of the C6H5 + O2 reaction, furan, could be formed through unimolecular decomposition of 1-oxo-n-butadienyl. Both the n-C4H5 + O2 reaction and unimolecular decomposition of its 1-oxo-n-butadienyl primary product are shown not to be a substantial source of ketene.

Differentiation of alkyl radicals: A route through chemical graph theory

AbstractAlkyl radicals play important roles such as intermediary metabolism, cell damage/injury and death leading to potential mutations. The present investigation using chemical graph theory studied two sets of carboxyl radicals, that is, deprotonated (DPro, radical) and protonated (Pro, radical anion) forms of 5‐ethyl heptanoic acid and 5‐ethenyl hept‐6‐enoic acid (Set I) radicals and 6‐ethyl octanoic acid and 6‐ethenyl oct‐7‐enoic acid (Set II) radicals. The study reveals that the largest eigenvalue (LEV) spectra of the adjacency matrix have a unique value, where the spectra increase from DPro to Pro and from single to double bonded alkyl radical structures, thus forming a scoring function for molecular topological indices. This topological index is presented as a measure for molecular connectivity/branching, where the index is used to predict the refractivity of a series of carboxyl radicals. The statistical correlation coefficient obtained for quantitative structure–property relationship between chemical structure (alkyl radical) and its physical property (refractivity) through heat maps are excellent and ranges within 0.97–0.99. It is further discovered that the vector component of the LEV gives an insight to its structural details, where it captures the node with the highest degree along with the important weighted node, that holds the complete structure (i.e., the radical site), in case of the Pro radical structures. Node centrality, which captures the structural makeup, divides DPro radical T‐shaped structures into two subunits for the signal transduction of important biological process like oral toxicity. Size of the largest clusters is also studied, illustrating the parameter to be less sensitive for differentiating the CC double bonds in the Pro radicals. To our knowledge, this is the first study where pattern recognition has been exemplified through the lower‐diagonal‐upper decomposition matrix of the chemical graph that forms a fingerprint signature to differentiate the alkyl radicals. The present study innovatively digitalizes the chemical structures of alkyl radicals that enables the discovery of structure–property relationship reflected by their molecular branching through machine learning.

Matrix-dependent a/x pair and overdegraded w/y/z ions generated by radical-directed dissociation of peptide radical cations [M]+ in matrix-assisted laser desorption/ionization in-source decay.

Fragmentation of peptide radical cations [M]. + has been examined using matrix-assisted laser desorption/ionization (MALDI) in-source decay (ISD) with hydrogen-abstracting nitro-substituted matrices. The ISD spectra of peptides containing an arginine (Arg) residue at carboxyl (C)-termini showed preferential [w]+ ions when 4-nitro-1-naphthol (4,1-NNL) matrix was used, whereas the use of 3,5-dinitrosalicylic acid (3,5-DNSA) resulted in preferential [x]+ ions. Minor or some [d]+ , [x]+ , [y]+ , and [z]+ ions were also observed. For peptides containing Arg residue at amino (N)-termini, the ISD spectra showed preferential [a]+ ions independent of matrix used. The observed [a]+ , [w]+ , [x]+ , [y]+ , and [z]+ ions can be rationally explained by radical-directed dissociation (RDD) of the peptide radical cations [M]. + , although [d]+ ions may be formed via Norrish Type I cleavage and/or by RDD of [M]. + ions. The formation of overdegraded [d]+ , [w]+ , [y]+ , and [z]+ ions is discussed from the standpoint of the internal energy of radical cations [M]. + and radical fragment ions [a + H]. + and [x + H]. + deposited via collisional interactions with excited matrix molecules in the MALDI plume. The radical site of the peptide cations [M]. + was presumed to be backbone amide nitrogen, from MALDI-ISD data with three different deuterated amino acids.

Radiation-Grafted Polymer Electrolyte Membranes for Fuel Cells

Fuel cells are one of the most efficient energy conversion systems to produce electricity. A solid ion-conducting polymer membrane is employed as both separator and electrolyte for polymer electrolyte membrane fuel cells and anion-exchange membrane fuel cells. Radiation-induced graft polymerization is a versatile method for the fabrication of low-cost alternatives to commercial polymer membranes. In this method, typically a base polymer is exposed to ionizing radiation which generates active radical sites within the polymer substrate. Then a suitable vinyl monomer is polimerized on these active sites to form a graft copolymer. Finally, a subsequent chemical treatment is performed to introduce hydrophilic groups to hydrophobic polymer backbone so that an ion conducting membrane is formed. There are various studies about the influence of radiation grafting parameters on membrane properties. Moreover, the favorable fuel cell relevant and polarization properties of such radiation-grafted membranes were reported. Thus, radiation-grafted polymer membranes are one of the significant low-cost alternatives for fuel cells. This review focuses on the preparation, characterization of fuel cell relevant properties and fuel cell performance of radiation-grafted membranes.