Thwarted Belonging and Perceived Burdensomeness During Middle and Older Adulthood: The Role of Generativity.

Using a sample of middle-aged and older adults, this research explores associations between generativity and two key risk factors for suicide: thwarted belonging (T.B.) and perceived burdensomeness (P.B.). These variables are typically studied as predictors of suicide; the current study is unique in examining their psychosocial correlates. Erikson described, generativity as a psychosocial construct that characterizes adult well-being in mid-life, conceptualized as the sense one has successfully guided and contributed to the younger generation through mentoring. Using the Midlife in the United States Survey (MIDUS), the current analyses indicate that generativity is associated with lower levels of P.B. and T.B., even after accounting for measures of hopelessness, depressive symptoms, financial stability, perceived neighborhood quality, chronic health conditions, and respondent's demographic characteristics including gender and age. Results are discussed in terms of applications for suicide-risk prevention, and with regard to the promotion of positive psychosocial development across the lifespan.

Developmental Changes in the Relation between Youth Disclosure and Parenting Behavior: A Cohort-sequential Analysis.

To address a gap in the literature regarding the development of youth disclosure across the transition to adolescence, the current research uses a cohort-sequential approach to study youth disclosure from middle childhood through adolescence. Longitudinal data from three cohorts of parents were utilized (N = 1359; children at T1 were in grades 2 [M = 8.00 years, SD = 0.57 years, 45% female], 4 [M = 10.12 years, SD = 0.60 years, 45% female], and 9 [M = 15.19 years, SD = 0.57 years, 48% female]). Parents were assessed annually over a 3-year time period. The focal analyses explored contemporaneous associations between characteristics of the parent-youth relationship (specifically, parental rejection and parental consistent discipline) and youth disclosure after accounting for person-specific trajectories of disclosure. Associations of gender, age, and socioeconomic status with disclosure were also assessed. Regarding trajectories of youth disclosure, results indicate that youth disclose less information to their parents about their daily lives as they get older; this trend was consistent across gender and socioeconomic status. In terms of associations with youth disclosure, when parents provided more consistent discipline or engaged in less rejection of their child, youth disclosure increased, even after accounting for their own trajectory of disclosure across time. In addition, the association of consistent discipline with youth disclosure became stronger with increased youth age. Results are discussed in terms of implications for understanding youth autonomy development, and the dyadic and developmental impact of parenting behaviors over time.

Sibling Adjustment to Childhood Chronic Illness: An Integrative Review.

Siblings of children with a chronic illness are among the close family members impacted by childhood chronic illness. Family roles, routines, and functioning are adjusted to fit the needs of the child and family throughout the course of the illness. Empirical articles regarding adjustment of healthy siblings of children with chronic illnesses ages 0 to 17 years, published in 2000 to 2019 were searched on PsycInfo, PubMed, and Medline using the keywords "sibling adjustment," "sibling chronic," and "sibling illness." Through thematic synthesis, four broad topics emerged concerning sibling adjustment to chronic illness: (a) experiences, (b) psychosocial adjustment, (c) coping, and (d) communication. Implications for family nursing and family health practitioners and future research directions are presented.

Sources of social support and gender in perceived stress and individual adjustment among Latina/o college-attending emerging adults.

OBJECTIVES: We explored the role of particular sources of social support (friends, romantic partners, family) as moderators and mediators in the associations between perceived stress and individual well-being (loneliness, depressive symptoms, and self-rated physical health). We also tested the possible moderating effect of gender to ascertain whether women and men are differentially impacted by social support's diverse sources. METHOD: Participants were 163 Latina/o emerging adults attending college (85% women; Mage = 20.2 years, range: 18-25). RESULTS: Holding perceived stress constant, friend support was negatively associated with loneliness, romantic partner support was negatively related to depressive symptoms, and family support was positively associated with self-rated physical health. Friend or romantic partner support moderated the relationships between perceived stress and loneliness, and self-rated physical health, but not depressive symptoms. Perceived stress and loneliness were indirectly and positively associated through lower friends and romantic partner supports, perceived stress and depressive symptoms were indirectly and positively related through lower romantic partner support, and perceived stress and self-rated physical health were related indirectly and negatively through lower family support. Gender moderated the relationships between family and friend support and self-rated physical health, and between friend support and depressive symptoms. Particular sources of support mediated the associations of perceived stress with well-being. CONCLUSIONS: Results highlight how social support helps Latina/o youth cope with stress and mitigate challenges associated with their college transition. Social support implications for physical and psychological health differ for male and female Latina/o college-attending emerging adults. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Nitrogen Dioxide Reaction with Nitroxide Radical Derived from Hydroxamic Acids: The Intermediacy of Acyl Nitroso and Nitroxyl (HNO).

Hydroxamic acids (RC(O)NHOH) form a class of compounds that display interesting chemical and biological properties The chemistry of RC(O)NHOH) is associated with one- and two-electron oxidations forming the respective nitroxide radical (RC(O)NHO•) and acyl nitroso (RC(O)N═O), respectively, which are relatively unstable species. In the present study, the kinetics and mechanism of the •NO2 reaction with nitroxide radicals derived from acetohydroxamic acid, suberohydroxamic acid, benzohydroxamic acid, and suberoylanilide hydroxamic acid have been studied in alkaline solutions. Ionizing radiation was used to generate about equal yields of these radicals, demonstrating that the oxidation of the transient nitroxide radical by •NO2 produces HNO and nitrite at about equal yields. The rate constant of •NO2 reaction with the nitroxide radical derived from acetohydroxamic acid has been determined to be (2.5 ± 0.5) × 109 M-1 s-1. This reaction forms a transient intermediate absorbing at 314 nm, which decays via a first-order reaction whose rate increases upon increasing the pH or the hydroxamic acid concentration. Transient intermediates absorbing around 314 nm are also formed during the oxidation of hydroxamic acids by H2O2 catalyzed by horseradish peroxidase. It is shown that HNO is formed during the decomposition of these intermediates, and therefore, they are assigned to acyl nitroso compounds. This study provides for the first time a direct spectrophotometric detection of acyl nitroso compounds in aqueous solutions allowing the study of their chemistry and reaction kinetics.

Direct Observation of Acyl Nitroso Compounds in Aqueous Solution and the Kinetics of Their Reactions with Amines, Thiols, and Hydroxamic Acids.

Acyl nitroso compounds or nitrosocarhonyls (RC(O)N═O) are reactive short-lived electrophiles, and their hydrolysis and reactions with nucleophiles produce HNO. Previously, direct detection of acyl nitroso species in nonaqueous media has been provided by time-resolved infrared spectroscopy demonstrating that its half-life is about 1 ms. In the present study hydroxamic acids (RC(O)NHOH) are oxidized electrochemically in buffered aqueous solutions (pH 5.9-10.2) yielding transient species characterized by their maximal absorption at 314-330 nm. These transient species decompose via a first-order reaction yielding mainly HNO and the respective carboxylic acid and therefore are ascribed to RC(O)N═O. The sufficiently long half-life of RC(O)N═O in aqueous solution allows for the first time the study of the kinetics of its reactions with various nucleophiles demonstrating that the nucleophilic reactivity follows the order thiolate > hydroxamate > amine. Metal chelates of CH3C(O)NHOH catalyze the hydrolysis of CH3C(O)N═O at the efficacy order of CuII > ZnII > NiII > CoII where only CuII catalyzes the hydrolysis also in the absence of the hydroxamate. Finally, oxidation of hydroxamic acids generates HNO, and the rate of this process is determined by the half-life of the respective acyl nitroso compound.

A longitudinal examination of social connectedness and suicidal thoughts and behaviors among adolescents.

BACKGROUND: This study examines the relationship between three different types of social connectivity and suicidal thoughts and behaviors. METHODS: Using the Add Health dataset, three domains of social connection were explored: parental connection, school connection, and social integration. Logistic regression was used to examine whether changes over time in connectedness predicted suicidal thoughts and behavior. RESULTS: Youth whose difference scores on social integration and parental connectedness increased were less likely to experience suicidal ideation. Increases in difference scores for perceived school connectedness protected youth who reported ideation from engaging in a suicide attempt. CONCLUSIONS: Perceptions of social connection are key factors in understanding adolescent suicidal thoughts and behaviors. It is important to consider social connection across different relationship contexts.

Nitroxide radicals as research tools: Elucidating the kinetics and mechanisms of catalase-like and "suicide inactivation" of metmyoglobin.

BACKGROUND: Metmyoglobin (MbFe(III)) reaction with H(2)O(2) has been a subject of study over many years. H(2)O(2) alone promotes heme destruction frequently denoted "suicide inactivation," yet the mechanism underlying H(2)O(2) dismutation associated with MbFe(III) inactivation remains obscure. METHODS: MbFe(III) reaction with excess H(2)O(2) in the absence and presence of the nitroxide was studied at pH 5.3-8.1 and 25°C by direct determination of reaction rate constants using rapid-mixing stopped-flow technique, by following H(2)O(2) depletion, O(2) evolution, spectral changes of the heme protein, and the fate of the nitroxide by EPR spectroscopy. RESULTS: The rates of both H(2)O(2) dismutation and heme inactivation processes depend on [MbFe(III)], [H(2)O(2)] and pH. Yet the inactivation stoichiometry is independent of these variables and each MbFe(III) molecule catalyzes the dismutation of 50±10 H(2)O(2) molecules until it is inactivated. The nitroxide catalytically enhances the catalase-like activity of MbFe(III) while protecting the heme against inactivation. The rate-determining step in the absence and presence of the nitroxide is the reduction of MbFe(IV)O by H(2)O(2) and by nitroxide, respectively. CONCLUSIONS: The nitroxide effects on H(2)O(2) dismutation catalyzed by MbFe(III) demonstrate that MbFe(IV)O reduction by H(2)O(2) is the rate-determining step of this process. The proposed mechanism, which adequately fits the pro-catalytic and protective effects of the nitroxide, implies the intermediacy of a compound I-H(2)O(2) adduct, which decomposes to a MbFe(IV)O and an inactivated heme at a ratio of 25:1. GENERAL SIGNIFICANCE: The effects of nitroxides are instrumental in elucidating the mechanism underlying the catalysis and inactivation routes of heme proteins.

The Suramin Derivative NF449 Interacts with the 5-fold Vertex of the Enterovirus A71 Capsid to Prevent Virus Attachment to PSGL-1 and Heparan Sulfate.

NF449, a sulfated compound derived from the antiparasitic drug suramin, was previously reported to inhibit infection by enterovirus A71 (EV-A71). In the current work, we found that NF449 inhibits virus attachment to target cells, and specifically blocks virus interaction with two identified receptors--the P-selectin ligand, PSGL-1, and heparan sulfate glycosaminoglycan--with no effect on virus binding to a third receptor, the scavenger receptor SCARB2. We also examined a number of commercially available suramin analogues, and newly synthesized derivatives of NF449; among these, NF110 and NM16, like NF449, inhibited virus attachment at submicromolar concentrations. PSGL-1 and heparan sulfate, but not SCARB2, are both sulfated molecules, and their interaction with EV-A71 is thought to involve positively charged capsid residues, including a conserved lysine at VP1-244, near the icosahedral 5-fold vertex. We found that mutation of VP1-244 resulted in resistance to NF449, suggesting that this residue is involved in NF449 interaction with the virus capsid. Consistent with this idea, NF449 and NF110 prevented virus interaction with monoclonal antibody MA28-7, which specifically recognizes an epitope overlapping VP1-244 at the 5-fold vertex. Based on these observations we propose that NF449 and related compounds compete with sulfated receptor molecules for a binding site at the 5-fold vertex of the EV-A71 capsid.

Nitroxides protect horseradish peroxidase from H2O2-induced inactivation and modulate its catalase-like activity.

BACKGROUND: Horseradish peroxidase (HRP) catalyzes H2O2 dismutation while undergoing heme inactivation. The mechanism underlying this process has not been fully elucidated. The effects of nitroxides, which protect metmyoglobin and methemoglobin against H2O2-induced inactivation, have been investigated. METHODS: HRP reaction with H2O2 was studied by following H2O2 depletion, O2 evolution and heme spectral changes. Nitroxide concentration was followed by EPR spectroscopy, and its reactions with the oxidized heme species were studied using stopped-flow. RESULTS: Nitroxide protects HRP against H2O2-induced inactivation. The rate of H2O2 dismutation in the presence of nitroxide obeys zero-order kinetics and increases as [nitroxide] increases. Nitroxide acts catalytically since its oxidized form is readily reduced to the nitroxide mainly by H2O2. The nitroxide efficacy follows the order 2,2,6,6-tetramethyl-piperidine-N-oxyl (TPO)>4-OH-TPO>3-carbamoyl proxyl>4-oxo-TPO, which correlates with the order of the rate constants of nitroxide reactions with compounds I, II, and III. CONCLUSIONS: Nitroxide catalytically protects HRP against inactivation induced by H2O2 while modulating its catalase-like activity. The protective role of nitroxide at µM concentrations is attributed to its efficient oxidation by P940, which is the precursor of the inactivated form P670. Modeling the dismutation kinetics in the presence of nitroxide adequately fits the experimental data. In the absence of nitroxide the simulation fits the observed kinetics only if it does not include the formation of a Michaelis-Menten complex. GENERAL SIGNIFICANCE: Nitroxides catalytically protect heme proteins against inactivation induced by H2O2 revealing an additional role played by nitroxide antioxidants in vivo.

Nitrite Reduction to Nitrous Oxide and Ammonia by TiO2 Electrons in a Colloid Solution via Consecutive One-Electron Transfer Reactions.

The mechanism of nitrite reduction by excess electrons on TiO2 nanoparticles (eTiO2(-)) was studied under anaerobic conditions. TiO2 was loaded with up to 75 electrons per particle, induced by γ-irradiation of acidic TiO2 colloid solutions containing 2-propanol. Time-resolved kinetics and material analysis were performed, mostly at 1.66 g L(-1) TiO2. At relatively low nitrite concentrations (R = [eTiO2(-)]o/[nitrite]o > 1.5), eTiO2(-) decays via two consecutive processes; at higher concentrations, only one decay step is observed. The stoichiometric ratio Δ[eTiO2(-)]/[nitrite]o of the faster process is about 2. This process involves the one-electron reduction of nitrite, forming the nitrite radical (k1 = (2.0 ± 0.2) × 10(6) M(-1) s(-1)), which further reacts with eTiO2(-) (k2) in competition with its dehydration to nitric oxide (NO) (k3). The ratios k2/k3 = (3.0 ± 0.5) × 10(3) M(-1) and k2 > 1 × 10(6) M(-1) s(-1) were derived from kinetic simulations and product analysis. The major product of this process is NO. The slower stage of the kinetics involves the reduction of NO by eTiO2(-), and the detailed mechanism of this process has been discussed in our earlier publication. The results reported in this study suggest that several intermediates, including NO and NH2OH, are adsorbed on the titanium nanoparticles and give rise to inverse dependency of the respective reaction rates on the TiO2 concentration. It is demonstrated that the reduction of nitrite by eTiO2(-) yields mainly N2O and NH3 via consecutive one-electron transfer reactions.

Loneliness, Stress, and Social Support in Young Adulthood: Does the Source of Support Matter?

Social support protects individuals against adversity throughout the lifespan, and is especially salient during times of intense social change, such as during the transition to adulthood. Focusing on three relationship-specific sources of social support (family, friends, and romantic partners), the current study examined the stress-buffering function of social support against loneliness and whether the association between social support and loneliness with stress held constant would vary by its source. The role of gender in these associations was also considered. The sample consisted of 636 ethnically diverse college youth (age range 18-25; 80 % female). The results suggest that the stress-buffering role of social support against loneliness varies by its source. Only support from friends buffered the association between stress and loneliness. Further, when stress was held constant, the association between social support and loneliness differed by the sources, in that support from friends or romantic partners (but not from family) was negatively associated with loneliness. Regarding gender differences, the adverse impact of lower levels of familial or friends' support on loneliness was greater in females than in males. This research advances our understanding of social support among college-aged youth; implications of the findings and directions for future research are discussed.

Nitric oxide reduction to ammonia by TiO2 electrons in colloid solution via consecutive one-electron transfer steps.

The reaction mechanism of nitric oxide (NO) reduction by excess electrons on TiO2 nanoparticles (e(TiO2)(-)) has been studied under anaerobic conditions. TiO2 was loaded with 10-130 electrons per particle using γ-irradiation of acidic TiO2 colloid solutions containing 2-propanol. The study is based on time-resolved kinetics and reactants and products analysis. The reduction of NO by e(TiO2)(-) is interpreted in terms of competition between a reaction path leading to formation of NH3 and a path leading to N2O and N2. The proposed mechanism involves consecutive one-electron transfers of NO, and its reduction intermediates HNO, NH2O(•), and NH2OH. The results show that e(TiO2)(-) does not reduce N2O and N2. Second-order rate constants of e(TiO2)(-) reactions with NO (740 ± 30 M(-1) s(-1)) and NH2OH (270 ± 30 M(-1) s(-1)) have been determined employing the rapid-mixing stopped-flow technique and that with HNO (>1.3 × 10(6) M(-1) s(-1)) was derived from fitting the kinetic traces to the suggested reaction mechanism, which is discussed in detail.

The chemistry and biological activities of N-acetylcysteine.

BACKGROUND: N-acetylcysteine (NAC) has been in clinical practice for several decades. It has been used as a mucolytic agent and for the treatment of numerous disorders including paracetamol intoxication, doxorubicin cardiotoxicity, ischemia-reperfusion cardiac injury, acute respiratory distress syndrome, bronchitis, chemotherapy-induced toxicity, HIV/AIDS, heavy metal toxicity and psychiatric disorders. SCOPE OF REVIEW: The mechanisms underlying the therapeutic and clinical applications of NAC are complex and still unclear. The present review is focused on the chemistry of NAC and its interactions and functions at the organ, tissue and cellular levels in an attempt to bridge the gap between its recognized biological activities and chemistry. MAJOR CONCLUSIONS: The antioxidative activity of NAC as of other thiols can be attributed to its fast reactions with OH, NO2, CO3(-) and thiyl radicals as well as to restitution of impaired targets in vital cellular components. NAC reacts relatively slowly with superoxide, hydrogen-peroxide and peroxynitrite, which cast some doubt on the importance of these reactions under physiological conditions. The uniqueness of NAC is most probably due to efficient reduction of disulfide bonds in proteins thus altering their structures and disrupting their ligand bonding, competition with larger reducing molecules in sterically less accessible spaces, and serving as a precursor of cysteine for GSH synthesis. GENERAL SIGNIFICANCE: The outlined reactions only partially explain the diverse biological effects of NAC, and further studies are required for determining its ability to cross the cell membrane and the blood-brain barrier as well as elucidating its reactions with components of cell signaling pathways.

The mechanism underlying nitroxyl and nitric oxide formation from hydroxamic acids.

BACKGROUND: The pharmacological effects of hydroxamic acids (RC(O)NHOH, HX) are partially attributed to their ability to serve as HNO and/or NO donors under oxidative stress. Given the development and use of HXs as therapeutic agents, elucidation of the oxidation mechanism is needed for more educated selection of HX-based drugs. METHODS: Acetohydroxamic and glycine-hydroxamic acids were oxidized at pH 7.0 by a continuous flux of radiolytically generated (·)OH or by metmyoglobin and H(2)O(2) reactions system. Gas chromatography and spectroscopic methods were used to monitor the accumulation of N(2)O, N(2), nitrite and hydroxylamine. RESULTS: Oxidation of HXs by (·)OH under anoxia yields N(2)O, but not nitrite, N(2) or hydroxylamine. Upon the addition of H(2)O(2) to solutions containing HX and metmyoglobin, which is instantaneously and continuously converted into compound II, nitrite and, to a lesser extent, N(2)O are accumulated under both anoxia and normoxia. CONCLUSIONS: Oxidation of HXs under anoxia by a continuous flux of (·)OH, which solely oxidizes the hydroxamate moiety to RC(O)NHO(·), forms HNO. This observation implies that bimolecular decomposition of RC(O)NHO(·) competes efficiently with unimolecular decomposition processes such as internal disproportionation, hydrolysis or homolysis. Oxidation by metmyoglobin/H(2)O(2) involves relatively mild oxidants (compounds I and II). Compound I reacts with HX forming RC(O)NHO(·) and compound II, which oxidizes HX, RC(O)NHO(·), HNO and NO. The latter reaction is the main source of nitrite. GENERAL SIGNIFICANCE: HXs under oxidative stress release HNO, but can be considered as NO-donors provided that HNO oxidation is more efficient than its reaction with other biological targets.

Perturbation analysis of heterochromatin-mediated gene silencing and somatic inheritance.

Repetitive sequences in eukaryotic genomes induce chromatin-mediated gene-silencing of juxtaposed genes. Many components that promote or antagonize silencing have been identified, but how heterochromatin causes variegated and heritable changes in gene expression remains mysterious. We have used inducible mis-expression in the Drosophila eye to recover new factors that alter silencing caused by the bw(D) allele, an insertion of repetitive satellite DNA that silences a bw(+) allele on the homologous chromosome. Inducible modifiers allow perturbation of silencing at different times in development, and distinguish factors that affect establishment or maintenance of silencing. We find that diverse chromatin and RNA processing factors can de-repress silencing. Most factors are effective even in differentiated cells, implying that silent chromatin remains plastic. However, over-expression of the bantam microRNA or the crooked-legs (crol) zinc-finger protein only de-repress silencing when expressed in cycling cells. Over-expression of crol accelerates the cell cycle, and this is required for de-repression of silencing. Strikingly, continual over-expression of crol converts the speckled variegation pattern of bw(D) into sectored variegation, where de-repression is stably inherited through mitotic divisions. Over-expression of crol establishes an open chromatin state, but the factor is not needed to maintain this state. Our analysis reveals that active chromatin states can be efficiently inherited through cell divisions, with implications for the stable maintenance of gene expression patterns through development.

The XNP remodeler targets dynamic chromatin in Drosophila.

Heterochromatic gene silencing results from the establishment of a repressive chromatin structure over reporter genes. Gene silencing is often variegated, implying that chromatin may stochastically switch from repressive to permissive structures as cells divide. To identify remodeling enzymes involved in reorganizing heterochromatin, we tested 11 SNF2-type chromatin remodelers in Drosophila for effects on gene silencing. Overexpression of five remodelers affects gene silencing, and the most potent de-repressor is the alpha-thalassaemia mental retardation syndrome X-linked (ATRX) homolog X-linked nuclear protein (XNP). Although the mammalian ATRX protein localizes to heterochromatin, Drosophila XNP is not a general component of heterochromatin. Instead, XNP localizes to active genes and to a major focus near the heterochromatin of the X chromosome. The XNP focus corresponds to an unusual decondensed satellite DNA block, and both active genes and the XNP focus are sites of ongoing nucleosome replacement. We suggest that the XNP remodeler modulates nucleosome dynamics at its target sites to limit chromatin accessibility. Although XNP at active genes may contribute to gene silencing, we find that a single focus is present across Drosophila species and that perturbation of this site cripples heterochromatic gene silencing. Thus, the XNP focus appears to be a functional genetic element that can contribute to gene silencing throughout the nucleus.

"People Think It's Easy Because I Smile, But It's Not Easy": The Lived Experiences of Six African American Single Mothers.

Grounded in Resilience Theory (Masten et al., 1990; Walsh, 1996; Walsh, 2002; Walsh, 2003) with a specific focus on parental resilience (Gavidia-Payne et al., 2015), this qualitative phenomenological study explored the lived experiences of low-income Female adult single parent (FASP) families. Each family had at least one adolescent aged 11 through 21 enrolled in special education classes and engaging in risk behaviors. Two central research questions were addressed. The first focused on the lived experiences of FASP and the second focused on their perspectives on how schools can enhance their support. Data were collected through face-to-face, in-depth, semi-structured interviews. Three major themes emerged: Life adjustment, The child is the priority, and Perseverance revealing their experience to be one of resilience. Participants also shared and provided insight on their perspectives regarding how schools can better support families. Findings revealed limited parent-school collaboration and highlight the need for further research with this population in the context of resilience. Suggestions for schools and communities working with such families are discussed.

One-electron reduction of 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin: a pulse radiolysis study.

Geldanamycin, a benzoquinone ansamycin antibiotic, is a natural product inhibitor of Hsp90 with potent and broad anticancer properties but with unacceptable levels of hepatotoxicity. Consequently, numerous structural analogs, which differ only in their 17-substituent, have been synthesized including the water-soluble and less toxic 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG, Alvespimycin). It has been suggested that the different hepatotoxicity reflects the redox active properties of the quinone moiety. The present pulse radiolysis study was aimed at studying the one-electron reduction of 17-DMAG. The UV-visible spectrum of the semiquinone radical, its pK(a), and the second-order rate constants for the reactions of 17-DMAG with CO(2)(•-) and (CH(3))(2)C(•)OH have been obtained. The reduction potential of 17-DMAG has been determined to be -194 ± 6 mV (vs NHE) using oxygen, 1,4-naphthoquinone, and menadione as electron acceptors. This reduction potential is lower than that of O(2) demonstrating that thermodynamically the semiquinone radical can reduce O(2) to superoxide, particularly since the concentration of O(2) is expected to exceed that of the drug in cells and tissues.

One-electron oxidation of acetohydroxamic acid: the intermediacy of nitroxyl and peroxynitrite.

The pharmacological effects of hydroxamate derivatives have been attributed not only to metal chelation or enzyme inhibition but also to their ability to serve as nitroxyl (HNO/NO(-)) and nitric oxide (NO) donors. However, the mechanism underlying the formation of these reactive nitrogen species is not clear and requires further elucidation. In the present study, one-electron oxidation of acetohydroxamic acid (aceto-HX) by (•)OH, (•)N(3), (•)NO(2), CO(3)(•-), and O(2)(•-) radicals was investigated using pulse radiolysis. It is demonstrated that only (•)OH, (•)N(3), and CO(3)(•-) radicals attack effectively and selectively the deprotonated form of the hydroxamate moiety, yielding the respective transient nitroxide radical. This nitroxide radical is a weak acid (CH(3)C(O)NHO(•), pK(a) = 9.1), which decays via a pH-dependent second-order reaction, 2k(2CH(3)C(O)NO(•-)) = (5.6 ± 0.4) × 10(7) M(-1) s(-1) (I = 0.002 M), 2k(CH(3)C(O)NO(•-) + CH(3)C(O)NHO(•)) = (8.3 ± 0.5) × 10(8) M(-1) s(-1)), and 2k(2CH(3)C(O)NHO(•)) = (8.7 ± 1.3) × 10(7) M(-1) s(-1). The second-order decomposition of the nitroxide yields transient species, one of which decomposes via a first-order reaction whose rate increases linearly upon increasing [CH(3)C(O)NHO(-)] or [OH(-)]. One-electron oxidation of aceto-HX under anoxia does not give rise to nitrite even after exposure to O(2), indicating that NO is not formed during the decomposition of the nitroxide radical. The presence of oxidants such as Tempol or O(2) during CH(3)C(O)NO(•-) decomposition had no effect on the reaction kinetics. Nevertheless, in the presence of Temopl, which does not react with NO but does with HNO, the formation of the hydroxylamine Tempol-H was observed. In the presence of O(2), about 60% of CH(3)C(O)NO(•-) yields ONOO(-), indicating that 30% NO(-) is formed in this system. It is concluded that under pulse radiolysis conditions, the transient nitroxide radicals derived from one-electron oxidation of aceto-HX decompose bimoleculary via a complex mechanism forming nitroxyl rather than NO.