Loss Of Group Research Articles

Study of spatial distributions of F, H and CF2 radicals in DF CCP discharge in Ar/CF4 and Ar/CHF3 mixtures

The comparative research of production and loss of atoms (F, H) and radicals (CF2), important for plasma processing, is carried out in DF CCP plasma in Ar/CF4 and Ar/CHF3 mixtures modeling two etching plasmas (fluorine-rich) and (fluorine-poor) respectively. Electron density, electron temperature and ion energy spectra are measured for single and dual frequency discharge modes. Spatial profiles of radical and atom densities are measured in both mixtures by using spatially resolved actinometry and UV absorption techniques. The opportunity for plasma-surface interaction control using spatial radical and atom density distributions is shown. The influence of high and low frequency powers on balance between surface and volume processes is discussed.

StarD4-mediated translocation of 7-hydroperoxycholesterol to isolated mitochondria: Deleterious effects and implications for steroidogenesis under oxidative stress conditions

StAR family proteins, including StarD4, play a key role in steroidogenesis by transporting cholesterol (Ch) into mitochondria for conversion to pregnenolone. Using a model system consisting of peroxidized cholesterol (7α-OOH)-containing liposomes as donors, we showed that human recombinant StarD4 accelerates 7α-OOH transfer to isolated liver mitochondria, and to a greater extent than Ch transfer. StarD4 had no effect on transfer of non-oxidized or peroxidized phosphatidylcholine, consistent with sterol ring specificity. StarD4-accelerated 7α-OOH transfer to mitochondria resulted in greater susceptibility to free radical lipid peroxidation and loss of membrane potential than in a non-StarD4 control. The novel implication of these findings is that in oxidative stress states, inappropriate StAR-mediated trafficking of peroxidized Ch in steroidogenic tissues could result in damage and dysfunction selectively targeted to mitochondria.

Potentiality or Capacity?— Agamben's Missing Subjects

Potentiality or Capacity?— Agamben's Missing Subjects Nina Power (bio) Discussions of the link between practice and action in European thought in recent years have come to resemble something of a merry-go-round, circulating between optimistic ontologies and pessimistic diagnoses, celebrations of passivity and predictions of activity. Changes in the nature of work and attempts to keep up with, diagnose or explain various forms of social resistance have seen the re-emergence of a curious pantheon of outsider literary figures - Kafka's Josephine the Mouse Singer, Melville's Bartleby, the Bible's Job.1 Work and its refusal are embodied in these troubled symbols of aesthetic excess (Josephine just wants to sing, not work like the other mice), obstinate potentiality (Bartleby's "I would prefer not to") and Job (the progressive withdrawal of all meaningful things and attachments). There is something minimal in all these figures, reduced to their ability to merely persist or to refuse in the last resort. We are reminded a little of Marx's early claims regarding "a class of civil society which is not a class of civil society… a total loss of humanity" which can only redeem itself through "the total redemption of humanity."2 But there is a crucial difference between Marx's universal class and these isolated, broken figures: the collective dimension is absent. Has contemporary philosophy become so withdrawn from organized struggle that it can only conceive of transformations in the attitude to work by recourse to minimal individuals? The last line of Bartleby the Scrivener: A Story of Wall Street may be "Ah, Bartleby! Ah humanity!" but this is more like a sigh of despair than a radical loss presaging redemption, political or otherwise. Is this all we can hope for? It is arguable that transformations in work and the composition of labor have made older, classically Marxist analysis seem outmoded, or at least in need of radical overhaul, but contemporary thought seems to have opted for two extreme responses: the radically pessimistic (or minimalist) or the baselessly optimistic. If Agamben falls into the former camp, then Hardt and Negri represent the latter with their concept of the multitude: The contemporary cooperative productive capacities through which the anthropological characteristics of the multitude are continually transcribed and reformulated, cannot help revealing a telos, a material affirmation of liberation.3 Just as it is altogether too quick to see the "material affirmation of liberation" in the exploitation of basic human capacities in work, it is altogether too slow to see in the obstinacy of a Bartleby the only response to sovereign domination. Agamben plays a central role in this recent "minimizing" turn, turning to an older Aristotelian concept of "potentiality" to explore, albeit paradoxically, the primacy of inactivity. In his discussion of Bartleby, he notes: "Our ethical tradition has often sought to avoid the problem of potentiality by reducing it to the terms of will and necessity… Bartleby is capable only without wanting."4 Agamben shares Heidegger's distaste for 'activity' and "will," deeming such concepts insuperably metaphysical. He thus demeans, unintentionally perhaps, the real forces at work in labor; Hardt and Negri, on the other hand, see all too clearly the politically productive elements of labor but miss crucial steps and antagonisms in the relation between production and emancipation. In the case of Hardt and Negri, this is perhaps a consequence of their affirmative ontology which sees potential everywhere. Agamben's paradoxical treatments of potentiality, on the other hand, seem to leave room only for reduced or promissory subjects. "The messianic concept of the remnant" may well permit "more than one analogy to be made with the Marxian proletariat"5 but only as "the unredeemable that makes salvation possible,"6 the part "with all due respect to those who govern us" that "never allows us to be reduced to a majority or a minority."7 There are other, far less deferential ways of conceiving of political opposition - do we need to say that all activity is necessarily metaphysical? Agamben's Aristotelian conception of potentiality entails, in the highest instance, "that potentiality constitutively be the potentiality not to (do or be)," which suggests that even if potential is realized, it is...

Metastable dimethyl phthalate molecular ions: Does the loss of a methoxyl radical proceed with or without anchimeric assistance?

Using MS/MS/MS experiments and quantum chemical calculations, it is demonstrated that oxygen (carbonyl) methylated phthalic anhydride cations are produced when metastable dimethyl phthalate molecular ions expel a methoxyl radical. At higher internal energies, isomeric acyl ions are competitively generated.

Insight into the Mechanism of Inactivation of Ribonucleotide Reductase by Gemcitabine 5′-Diphosphate in the Presence or Absence of Reductant

Gemcitabine 5'-diphosphate (F(2)CDP) is a potent inhibitor of ribonucleotide reductases (RNRs), enzymes that convert nucleotides (NDPs) to deoxynucleotides and are essential for DNA replication and repair. The Escherichia coli RNR, an alpha2beta2 complex, when incubated with 1 equiv of F(2)CDP catalyzes the release of two fluorides and cytosine concomitant with enzyme inactivation. In the presence of reductant (thioredoxin/thioredoxin reductase/NADPH or DTT), the enzyme inactivation results from its covalent labeling of alpha with the sugar of F(2)CDP (one label/alpha2beta2). SDS-PAGE analysis of the inactivated RNR without boiling of the sample reveals that alpha migrates as an 87 and 110 kDa protein in a ratio of 0.6:0.4. When the reductant is omitted, RNR is inactivated by loss of the essential tyrosyl radical and formation of a new radical. Inactivation studies with C225S-alpha in the presence or absence of reductants, reveal it behaves like wt-RNR in the absence of reductant. Inactivated C225S-alpha migrates as an 87 kDa protein and is not covalently modified. C225 is one of the cysteines in RNR's active site that supplies reducing equivalents to make dNDPs. To identify the new radical formed, [1'-(2)H]-F(2)CDP was studied with wt- and C225S-RNR by 9 and 140 GHz EPR spectroscopy. These studies revealed that the new radical is a nucleotide derived with g values of g(x) 2.00738, g(y) 2.00592, and g(z) 2.00230 and with altered hyperfine interactions (apparent triplet collapsed to a doublet) relative to [1'-(1)H]-F(2)CDP. The EPR features are very similar to those we recently reported for the nucleotide radical generated with CDP and E441Q-RNR.

Rates and regimes of photochemical ozone production over Central East China in June 2006: a box model analysis using comprehensive measurements of ozone precursors

Abstract. An observation-based box model approach was undertaken to estimate concentrations of OH, HO2, and RO2 radicals and the net photochemical production rate of ozone at the top of Mount Tai, located in the middle of Central East China, in June 2006. The model calculation was constrained by the measurements of O3, H2O, CO, NO, NO2, hydrocarbon, HCHO, and CH3CHO concentrations, and temperature and J values. The net production rate of ozone was estimated to be 6.4 ppb h−1 as a 6-h average (09:00–15:00 CST), suggesting 58±37 ppb of ozone is produced in one day. Thus the daytime buildup of ozone recorded at the mountain top as ~23 ppb on average is likely affected by in situ photochemistry as well as by the upward transport of polluted air mass in the daytime. On days with high ozone concentrations (hourly values exceeding 100 ppb at least once), in situ photochemistry was more active than it was on low ozone days, suggesting that in situ photochemistry is an important factor controlling ozone concentrations. Sensitivity model runs for which different NOx and hydrocarbon concentrations were assumed suggested that the ozone production occurred normally under NOx-limited conditions, with some exceptional periods (under volatile-organic-compound-limited conditions) in which there was fresh pollution. We also examined the possible influence of the heterogeneous loss of gaseous HO2 radicals in contact with aerosol particle surfaces on the rate and regimes of ozone production.

Collision induced dissociation of protonated N-nitrosodimethylamine by ion trap mass spectrometry: Ultimate carcinogens in gas phase

Collision induced dissociation of protonated N-nitrosodimethylamine (NDMA) and isotopically labeled N-nitrosodimethyl-d6-amine (NDMA-d6) was investigated by sequential ion trap mass spectrometry to establish mechanisms of gas phase reactions leading to intriguing products of this potent carcinogen. The fragmentation of (NDMA + H +) occurs via two dissociation pathways. In the alkylation pathway, homolytic cleavage of the N–O bond of N-dimethyl, N′-hydroxydiazenium ion generates N-dimethyldiazenium distonic ion which reacts further by a CH 3 radical loss to form methanediazonium ion. Both methanediazonium ion and its precursor are involved in ion/molecule reactions. Methanediazonium ion showed to be capable of methylating water and methanol molecules in the gas phase of the ion trap and N-dimethyldiazenium distonic ion showed to abstract a hydrogen atom from a solvent molecule. In the denitrosation pathway, a tautomerization of N-dimethyl, N′-hydroxydiazenium ion to N-nitrosodimethylammonium intermediate ion results in radical cleavage of the N–N bond of the intermediate ion to form N-dimethylaminium radical cation which reacts further through α-cleavage to generate N-methylmethylenimmonium ion. Although the reactions of NDMA in the gas phase are different to those for enzymatic conversion of NDMA in biological systems, each activation method generates the same products. We will show that collision induced dissociation of N-nitrosodiethylamine (NDEA) and N-nitrosodipropylamine (NDPA) is also a feasible approach to gain information on formation, stability, and reactivity of alkylating agents originating from NDEA and NDPA. Investigating such biologically relevant, but highly reactive intermediates in the condensed phase is hampered by the short life-times of these transient species.

1H NMR, 13C NMR and mass spectral studies of some Schiff bases derived from 3-amino-1,2,4-triazole

Heterocyclic Schiff bases derived from 3-amino-1,2,4-triazole and different substituted aromatic aldehydes are prepared and subjected to 1H NMR, 13C NMR and mass spectral analyses. 1H NMR spectra in DMSO exhibit a sharp singlet within the 9.35–8.90 ppm region which corresponds to the azomethine proton. The position of this signal is largely dependent on the nature of the substituents on the benzal moiety. It is observed that the shape, position and the integration value of the signal of the aromatic proton of the triazole ring ( 5C) are clearly affected by the rate of exchange, relaxation time, concentration of solution as well as the solvent used. 13C NMR is taken as substantial support for the results reached from 1H NMR studies. The mass spectral results are taken as a tool to confirm the structure of the investigated compounds. The base peak (100%), mostly the M-1 peak, indicates the facile loss of hydrogen radical. The fragmentation pattern of the unsubstituted Schiff base is taken as the general scheme. Differences in the other schemes result from the effect of the electronegativity of the substituents attached to the aromatic ring.

Dissociative Photoionization of X(CH3)3 (X = N, P, As, Sb, Bi): Mechanism, Trends, and Accurate Energetics

Threshold photoelectron photoion coincidence spectroscopy is used to study the dissociation of energy-selected X(CH(3))(3)(+) ions (X = As, Sb, Bi) by methyl loss, the only process observed up to 2 eV above the ionization energy. The ion time-of-flight distributions and the breakdown diagrams are analyzed in terms of the statistical RRKM theory to obtain accurate ionic dissociation energies. These experiments complement previous studies on analogous trimethyl compounds of the N group where X = N and P. However, trimethylamine was observed to lose only an H atom, whereas trimethylphosphine was shown to lose methyl radical, H atom, and, to a lesser extent, methane in parallel dissociation reactions. Both kinetic and thermodynamic arguments are needed to explain these trends. The methyl radical loss has two channels: either a H transfer to the central atom, followed by CH(3) loss, or a direct homolytic bond cleavage. However, the H transfer channel is blocked in trimethylamine by an H loss channel with an earlier onset, and, thus, the methyl loss is not observed. Bond energies are defined based on ab initio reaction energies and show that the main thermodynamic reason behind the trends in the energetics is the significantly weakening C=X double bond in the ion in the N --> As direction. The first adiabatic ionization energies of Sb(CH(3))(3) and Bi(CH(3))(3) have also been measured by ultraviolet photoelectron spectroscopy to be 8.02 +/- 0.05 and 8.08 +/- 0.05 eV, respectively.

Radical Moral Authority and Desire: The Image of the Male Romantic Poet in Frontispiece Portraits of Byron and Shelley

This paper considers the history and iconography of frontispiece portraits of Byron and Shelley from the late eighteenth to the nineteenth centuries. In particular, the paper argues that the frontispiece reproductions are products of a nexus of technological, cultural, and economic circumstances that in the nineteenth century would change the way that poetry was established and the emotional responses that poets evoked in their audiences. By eliciting in their viewers emotions associated with radical moral authority, vulnerability, and loss, the portraits portray the male Romantic poet as as the subversive/angelic prophet of social and secual reform whose image powerfully influenced the nineteenth-century construction of Romanticism.

Theoretical Mechanistic Study of the Oxidative Degradation of Benzene in the Troposphere: Reaction of Benzene-HO Radical Adduct with O2.

Competing pathways arising from the reaction of hydroxycyclohexadienyl radical (1) with O2, a key reaction in the oxidative degradation of benzene under tropospheric conditions, have been investigated by means of density functional theory (UB3LYP) and quantum-mechanical (UCCSD(T) and RCCSD(T)) electronic structure calculations. The energetic, structural, and vibrational results furnished by these calculations were subsequently used to perform conventional transition-state computations to predict the rate coefficients and evaluate the product yields. The trans stereoisomer of the peroxyl radical (4) produced by the O2 addition to position 2 of benzene ring in radical 1 is energetically more stable than the cis one, although the rate coefficients at 298 K for the formation of both isomers are predicted to be similar. The cyclization of the cis isomer of 4 to a bicyclic allyl radical (5) involves calculated barrier heights (ΔU(⧧), ΔE(⧧), ΔH(⧧), and ΔG(⧧)) significantly lower than those of the cyclization of the trans isomer of 4. This implies that the formation of the cis isomer of 4 can lead to irreversible loss of radical 1 and that the observed chemical equilibrium 1 + O2 ↔ 4 essentially involves the trans isomer of 4. Although the reaction enthalpies computed for the O2 addition to position 4 of benzene ring in radical 1, affording the cis and trans stereoisomers of a peroxyl radical (6), are similar to those for the addition to position 2, the latter addition mode is clearly preferred because it involves lower barrier heights. The barrier heights computed for the cyclization of either the cis or the trans isomers of 6 to a bicyclic radical bearing a peroxy bridge (7) are about twice those computed for the cyclization of either the cis or the trans isomers of 4. Thus, under tropospheric conditions, it is unlikely that the O2 addition to position 4 of the benzene ring in radical 1 can contribute to the formation of benzene oxidation products.

Radical gain and loss of CEACAM/PSG family genes in vertebrates

In placental mammals, a family of recently evolved tumor suppressor genes, carcinoembryonic antigen cell adhesion molecules (CEACAMs), and related pregnancy‐specific glycoproteins (PSGs) are critical to the regulation of tumorigenesis, fetal‐maternal interaction, and pathogen transmission. Despite having important roles in many basic physiological processes, these genes were believed to be "eutherian‐specific"; how they evolved remains a mystery. Based on syntenic mapping analyses, we reveal that, surprisingly, a large number of diverging CEACAM orthologs is present from teleosts to marsupial mammals. In addition, based on the deduced ancestral genotypes, we infer that the CEACAM gene family evolved from a couple of ancestral genes in the common ancestor of teleosts and tetrapods. Taken together, contrary to the conventional view that CEACAMs are placental mammal‐specific, our study reveals that CEACAM family genes represent an independent branch of the immunoglobulin superfamily that evolved early in vertebrates. Furthermore, while the observed accelerated gene gain of CEACAMs in therian mammals could be partly attributed to the presence of repetitive sequences and a lower genetic constraint associated with cell surface receptors, we propose an alternative evolution model to account for the radical changes in the CEACAM gene inventory.The abstract was partly supported by the Taiwan National Health Research Institute grant HMRPG380011 and the NIDDK grant DK70652.

Peroxy radicals in the summer free troposphere: seasonality and potential for heterogeneous loss

Abstract. The sum of peroxy radicals (HO2+ΣiRiO2) and supporting trace gases were measured on the Jungfraujoch (3580 m a.s.l.) during the late summer of 2005. The period was marked by extended times of heavy snow which led to reduction in the observed peroxy radicals during the snowy periods that was greater than the concomitant reduction in j(O1D). In the limit a first order loss rate of 0.0063 s−1 can be derived for the peroxy radical loss in the snowy conditions that could be potentially ascribed to a heterogenous loss process. On snow free days photolysis of HCHO is shown to be a significant peroxy radical source. The seasonal trends of the peroxy radical concentrations have been mapped from the winter to summer transition in line with previous experiments. Net ozone production in late summer at the Jungfraujoch was net neutral to marginally ozone destructive. A value of 28±4 pptv is calculated for the ozone compensation point for the snow free days.

Role of the Oxyferrous Heme Intermediate and Distal Side Adduct Radical in the Catalase Activity of Mycobacterium tuberculosis KatG Revealed by the W107F Mutant

Catalase-peroxidase (KatG) is essential in Mycobacterium tuberculosis for oxidative stress management and activation of the antitubercular pro-drug isoniazid. The role of a unique distal side adduct found in KatG enzymes, involving linked side chains of residues Met255, Tyr229, and Trp107 (MYW), in the unusual catalase activity of KatG is addressed here and in our companion paper (Suarez, J., Ranguelova, K., Jarzecki, A. A., Manzerova, J., Krymov, V., Zhao, X., Yu, S., Metlitsky, L., Gerfen, G. J., and Magliozzo, R. S. (2009) J. Biol. Chem. 284, in press). The KatG[W107F] mutant exhibited severely reduced catalase activity yet normal peroxidase activity, and as isolated contains more abundant 6-coordinate heme in high spin and low spin forms compared with the wild-type enzyme. Most interestingly, oxyferrous heme is also found in the purified enzyme. Oxyferrous KatG[W107F] was prepared by photolysis in air of the carbonyl enzyme or was generated using hydrogen peroxide decayed with a t1/2 of 2 days compared with 6 min for wild-type protein. The stability of oxyenyzme was modestly enhanced in KatG[Y229F] but was not affected in KatG[M255A]. Optical stopped-flow experiments showed rapid formation of Compound I in KatG[W107F] and facile formation of oxyferrous heme in the presence of micromolar hydrogen peroxide. An analysis of the relationships between catalase activity, stability of oxyferrous enzyme, and a proposed MYW adduct radical is presented. The loss of catalase function is assigned to the loss of the MYW adduct radical and structural changes that lead to greatly enhanced stability of oxyenzyme, an intermediate of the catalase cycle of native enzyme.

Photodissociation of vinyl cyanide at 193 nm: Nascent product distributions of the molecular elimination channels

The photodissociation dynamics of vinyl cyanide (H(2)CCHCN, acrylonitrile) and deuterated vinyl cyanide (D(2)CCDCN) at 193 nm are examined using time-resolved Fourier transform infrared emission spectroscopy. Prior photofragment translational spectroscopy studies [D. A. Blank et al., J. Chem. Phys. 108, 5784 (1998)] of the dissociation have observed the presence of four main dissociation channels; two molecular and two radical in nature. However, with the exception of a<0.01 quantum yield determined for the CN radical loss channel, the branching ratios of the remaining three elimination channels were not measured. The time-resolved emission spectra, including those from the deuterated samples, revealed the presence of acetylene, hydrogen cyanide (HCN), as well as the energetically less stable isomer hydrogen isocyanide (HNC). Acetylene is found in two distinct energetic distributions, suggesting that both three- and four-centered elimination reactions are occurring significantly in the dissociation. In contrast to prior ab initio studies that have suggested the dominant nature of the three-center elimination of molecular hydrogen (H(2)) and cyanovinylidene (:C=CHCN), we find this reaction channel to be of little importance as there is no evidence to support any significant presence of rovibrationally excited cyanoacetylene. Spectral modeling of the product distributions allows for the first experimental determination of the relative occurrence of the three-centered (resulting in HCN+vinylidene) versus four-centered (HNC+acetylene) elimination channels as 3.34 to 1.00, in contrast to the previously calculated value of 126:1. Rice-Ramsperger-Kassel-Marcus analysis depicts that the transition state energy of the four-centered reaction should be about 10 kcal mole(-1) lower than the three-centered reaction.

The complexity turn in studies of organisations and leadership: relevance and implications

The widespread experience of complexity is the experience of radical unpredictability and loss of clear connections between cause and effect. The typical response from leaders and researchers is to suggest that more complex contexts require new ways of management control and that particular ways of organising and leading are better than others in order to deal with this. However, the complexity orientation in organisational studies demonstrates that complexity is not a phenomenon that can be brought under control for subsequent analysis, manipulation and change from 'the outside'. What are the implications of this for the understanding of organisational dynamics and leadership? Complexity research is seeking to understand this by exploring what seems to be the core of the issue at hand: the interactional and paradoxical nature of leadership and organisational stability and change.

Radical loss of an extreme extra-pair mating system

BackgroundMating outside the pair-bond is surprisingly common in socially monogamous birds, but rates of extra-pair paternity (EPP) vary widely between species. Although differences in life-history and contemporary ecological factors may explain some interspecific variation, evolutionary forces driving extra-pair (EP) mating remain largely obscure. Also, since there is a large phylogenetic component to the frequency of EPP, evolutionary inertia may contribute substantially to observed EP mating patterns. However, the relative importance of plasticity and phylogenetic constraints on the incidence of EP mating remains largely unknown.ResultsWe here demonstrate very low levels of EPP (4.4% of offspring) in the purple-crowned fairy-wren Malurus coronatus, a member of the genus with the highest known levels of EPP in birds. In addition, we show absence of the suite of distinctive behavioral and morphological adaptations associated with EP mating that characterize other fairy-wrens. Phylogenetic parsimony implies that these characteristics were lost in one speciation event. Nonetheless, many life-history and breeding parameters that are hypothesized to drive interspecific variation in EPP are not different in the purple-crowned fairy-wren compared to its promiscuous congeners.ConclusionSuch radical loss of an extreme EP mating system with all associated adaptations from a lineage of biologically very similar species indicates that evolutionary inertia does not necessarily constrain interspecific variation in EPP. Moreover, if apparently minor interspecific differences regularly cause large differences in EPP, this may be one reason why the evolution of EP mating is still poorly understood.

A Fragmentation study of di-acidic mycosporine-like amino acids in electrospray and nanospray mass spectrometry

Two mycosporine (MAAs), containing an extra acid function, were analyzed by nanospray and electrospray ionization tandem mass spectrometry. In contrast to the previous studies it is demonstrated that no significant characteristic methyl radical loss occurred in positive mode. The fragmentation pathway in negative mode was also proposed in this work, along with theoretical calculations to characterize the site of protonation.

Structure of the nucleotide radical formed during reaction of CDP/TTP with the E441Q-alpha2beta2 of E. coli ribonucleotide reductase.

The Escherichia coli ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates to deoxynucleotides and requires a diferric-tyrosyl radical cofactor for catalysis. RNR is composed of a 1:1 complex of two homodimeric subunits: α and β. Incubation of the E441Q-α mutant RNR with substrate CDP and allosteric effector TTP results in loss of the tyrosyl radical and formation of two new radicals on the 200 ms to min time scale. The first radical was previously established by stopped flow UV/vis spectroscopy and pulsed high field EPR spectroscopy to be a disulfide radical anion. The second radical was proposed to be a 4′-radical of a 3′-keto-2′-deoxycytidine 5′-diphosphate. To identify the structure of the nucleotide radical [1′-2H], [2′-2H], [4′-2H], [5′-2H], [U−13C, 15N], [U−15N], and [5,6 -2H] CDP and [β-2H] cysteine-α were synthesized and incubated with E441Q-α2β2 and TTP. The nucleotide radical was examined by 9 GHz and 140 GHz pulsed EPR spectroscopy and 35 GHz ENDOR spectroscopy. Substitution of 2H at C4′ and C1′ altered the observed hyperfine interactions of the nucleotide radical and established that the observed structure was not that predicted. DFT calculations (B3LYP/IGLO-III/B3LYP/TZVP) were carried out in an effort to recapitulate the spectroscopic observations and lead to a new structure consistent with all of the experimental data. The results indicate, unexpectedly, that the radical is a semidione nucleotide radical of cytidine 5′-diphosphate. The relationship of this radical to the disulfide radical anion is discussed.

Time-Resolved Studies of CN Radical Reactions and the Role of Complexes in Solution

Time-resolved studies using 100 fs laser pulses generate CN radicals photolytically in solution and probe their subsequent reaction with solvent molecules by monitoring both radical loss and product formation. The experiments follow the CN reactants by transient electronic spectroscopy at 400 nm and monitor the HCN products by transient vibrational spectroscopy near 3.07 microm. The observation that CN disappears more slowly than HCN appears shows that the two processes are decoupled kinetically and suggests that the CN radicals rapidly form two different types of complexes that have different reactivities. Electronic structure calculations find two bound complexes between CN and a typical solvent molecule (CH(2)Cl(2)) that are consistent with this picture. The more weakly bound complex is linear with CN bound to an H atom through the N atom, and the more strongly bound complex has a structure in which the CN bridges Cl and H atoms of the solvent. Fitting the transient absorption data with a kinetic model containing two uncoupled complexes reproduces the data for seven different chlorinated alkane solvents and yields rate constants for the reaction of each type of complex. Depending on the solvent, the linear complex reacts between 2.5 and 12 times faster than the bridging complex and is the primary source of the HCN reaction product. Increasing the Cl atom content of the solvents decreases the reaction rate for both complexes.