Dibromo-BODIPY as an Organic Photocatalyst for Radical-Ionic Sequences.

A new dibrominated 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is reported as a new metal-free photocatalyst. This BODIPY showed similar optoelectronic, electrochemical, and performance properties to those of Ru(bpy)3Cl2, one of the most common photocatalysts in a known radical-ionic transformation, such as the formation of 1,4-dicarbonyl compounds. Moreover, additional sequences in which the generated oxonium ion is trapped by an internal nucleophile were developed using this BODIPY photocatalyst. These new sequences allowed the straightforward preparation of γ-alkoxylactones, monoprotected 1,4-ketoaldehydes, and dihydrofurans. This new catalyst, the methodology, and the forged functional groups could be important tools in organic synthesis.

Emotions and Reactions to the Confinement by COVID-19 of Children and Adolescents With High Abilities and Community Samples: A Mixed Methods Research Study.

The goal of this research is to know and compare the emotions and reactions to confinement due to the COVID-19 pandemic in children and adolescents with high abilities and community samples. This is a mixed study with an exploratory reach that is descriptive, and which combines survey and qualitative methodologies to examine the emotions and reactions to confinement experiences of children and adolescents aged between 5 and 14 years. An online poll was designed with 46 questions, grouped into three sections: (1) General Data, (2) Reactions to the health contingencies of COVID-19, and (3) Positive and negative emotions. This last section was included the Oros' positive emotions questionnaire (2014) and the scales of the negative effect of the PANAS Schedule positive and negative affect on children and adolescents between 8 and 14 years old (Sandin, 2003). Data were collected online with a convenience sample. Quantitative data were analyzed with the SPSS statistics program and qualitative data with Alceste software. Among the main findings is the fact that there are no significant differences between the groups by ability in terms of reactions and emotions; however, there are differences between age groups and sex. The study discusses the implications for educational intervention in situations like the current pandemic.

Effects of fear of crime on subjective well-being: a meta-analytic review / Los efectos del miedo al delito en el bienestar subjetivo: revisión metaanalítica

We analyzed 12 studies from North America, South America, Europe, and Oceania (New Zealand) on the association between fear of crime and subjective well-being. These studies gather data from 39 countries and 407,474 subjects. Heterogeneity was found between the studies. The random effect model showed an average effect of = -.15 (ρ = -.21). Two of the studies estimated fear of crime with a single generic question and five studies assessed subjective well-being through one item of satisfaction with life. Meta-regression showed that the effect was superior in younger samples, with affective measurement of well-being in comparison with cognitive ones, of mono-item (versus multi-items) and in the countries of Latin America, suggesting that in contexts of greater frequency and seriousness of the crime the fear of crime negatively affects subjective well-being. The diffuse or concrete nature of the measure of fear did not show a significant moderator effect. Limitations of the study and proposals for future research are discussed

Se analizaron 12 estudios de Norteamérica, Latinoamérica, Europa y Oceanía (Nueva Zelanda) con respecto a la asociación entre el miedo al delito y el bienestar subjetivo. Los estudios reúnen información de 39 países y 407,474 sujetos. Se encontró heterogeneidad entre los estudios. El modelo de efectos aleatorios mostró un efecto promedio de = -.15 (ρ = -.21). Dos estudios evaluaron el miedo al delito con una sola pregunta genérica, mientras que cinco estudios midieron el bienestar subjetivo con un ítem de satisfacción con la vida. La meta-regresión mostró que el efecto fue superior en muestras más jóvenes, con medidas afectivas del bienestar subjetivo en comparación con medidas cognitivas de un solo ítem (versus medidas poli-item), y en países de Latinoamérica, sugiriendo que en contextos de mayor frecuencia y severidad del crimen el miedo al delito afecta negativamente al bienestar subjetivo. La naturaleza difusa o concreta de la medida de miedo al delito no mostró un efecto moderador. Se debaten las limitaciones del estudio y las propuestas para futuras investigaciones

Extracurricular activities and group belonging as a protective factor in adolescence / Actividades extraescolares y pertenencia al grupo como factor protector en la adolescencia

In the transition into adulthood, family and school play a critical role protecting the adolescent from engaging in behaviors that could cause mental health problems. Nevertheless, there are other social groups and structured activities that have shown to act as an educational activity and as a protective factor as well. The aim of this study was to investigate the relationship between belonging to different types of social groups and the positive and negative mental health indicators of Mexican adolescents. Participants were 840 Mexican adolescents ranging between 12 and 17 years old. Results indicated that belonging to artistic and scout groups reported a statistically significant correlation with higher levels of emotional intelligence. Belonging to sport and artistic groups reported a statistically significant correlation with higher levels of resilience. No statistically significant results were found on anxiety, depression, and/or disruptive behaviors. Further research is needed, especially investigating possible predictive and moderating variables

En la transición a la vida adulta, la familia y la escuela juegan un papel protector decisivo para proteger al adolescente de comportamientos que podrían acarrearle problemas de salud mental. No obstante, hay otros grupos sociales y actividades estructuradas que han funcionado como actividades educativas además de como factores protectores. El objetivo de este trabajo ha sido investigar la relación entre la pertenencia a diferentes tipos de grupos sociales y los indicadores positivos y negativos de salud mental de adolescentes mexicanos. Los participantes eran 840 adolescentes mexicanos de edades comprendidas entre los 12 y los 17 años. Los resultados indican que la pertenencia a grupos artísticos y scouts correlacionaba significativamente con elevados niveles de inteligencia emocional. Pertenecer a grupos deportivos y artísticos correlacionaba significativamente con elevados niveles de resiliencia. No se dieron resultados estadísticamente significativos en ansiedad, depresión o conductas problemáticas. Se necesita continuar investigando, sobre todo en las posibles variables predictoras y moderadoras

Effect of phytotoxic secondary metabolites and semisynthetic compounds from endophytic fungus Xylaria feejeensis strain SM3e-1b on spinach chloroplast photosynthesis.

We investigated the mechanism of action on the photosynthesis light reactions of three major secondary metabolites produced by the endophytic fungus Xylaria feejeensis strain SM3e-1b, isolated from Sapium macrocarpum; and four novel derivatives of coriloxine, a major compound produced by X. feejeensis. The natural phytotoxins include one epoxycyclohexenone derivative, coriloxine (1), and two quinone derivatives (2-3). The semisynthetic derivatives of coriloxine are two cyclohexenone (4-6) and two quinone compounds (5-7). Cyclohexenone (4), (4R,5S,6R)-6-chloro-4,5-dihydroxy-3-methoxy-5-methylcyclohex-2-enone, inhibited ATP synthesis in freshly lysed spinach chloroplasts from water to MV; it also partly inhibited the basal and uncoupled photosynthetic electron transport, and significantly enhanced the phosphorylating electron transport and Mg2+-ATPase activity, thus demonstrating its action as an uncoupler agent. On the other hand, quinone (7), 2-((4-butylphenyl)amino)-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione, inhibited ATP synthesis, and non-cyclic electron transport from water to MV in basal, phosphorylating and uncoupled conditions in a concentration-dependent manner. Hence, (7) behaves as a Hill reaction inhibitor at the PSII electron transport on the water splitting enzyme (OEC), and on the acceptor side between P680 and QA. This mechanism of action was confirmed by chlorophyll a fluorescence measurements. These results indicate that coriloxine derivatives 4 and 7 could work as prototype structures for the development of new herbicides. Contrastingly, natural products 1-3, and derivatives 5 and 6 did not show a significant inhibitory effect on ATP synthesis.

Curcumin prevents mitochondrial dynamics disturbances in early 5/6 nephrectomy: Relation to oxidative stress and mitochondrial bioenergetics.

Five-sixths nephrectomy (5/6NX) is a widely used model to study the mechanisms leading to renal damage in chronic kidney disease (CKD). However, early alterations on renal function, mitochondrial dynamics, and oxidative stress have not been explored yet. Curcumin is an antioxidant that has shown nephroprotection in 5/6NX-induced renal damage. The aim of this study was to explore the effect of curcumin on early mitochondrial alterations induced by 5/6NX in rats. In isolated mitochondria, 5/6NX-induced hydrogen peroxide production was associated with decreased activity of complexes I and V, decreased activity of antioxidant enzymes, alterations in oxygen consumption and increased MDA-protein adducts. In addition, it was found that 5/6NX shifted mitochondrial dynamics to fusion, which was evidenced by increased optic atrophy 1 and mitofusin 1 (Mfn1) and decreased fission 1 and dynamin-related protein 1 expressions. These data were confirmed by morphological analysis and immunoelectron microscopy of Mfn-1. All the above-described mechanisms were prevented by curcumin. Also, it was found that curcumin prevented renal dysfunction by improving renal blood flow and the total antioxidant capacity induced by 5/6NX. Moreover, in glomeruli and proximal tubules 5/6NX-induced superoxide anion production by uncoupled nitric oxide synthase (NOS) and nicotinamide adenine dinucleotide phosphate oxidase (NOX) dependent way, this latter was associated with increased phosphorylation of serine 304 of p47phox subunit of NOX. In conclusion, this study shows that curcumin pretreatment decreases early 5/6NX-induced altered mitochondrial dynamics, bioenergetics, and oxidative stress, which may be associated with the preservation of renal function. © 2016 BioFactors, 43(2):293-310, 2017.

Synthesis, photophysical, electrochemical and electrochemiluminescence properties of A2B2 zinc porphyrins: the effect of π-extended conjugation.

The synthesis of two A2B2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc(ii) () and {5,15-bis-(carbazol-3-yl-ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc(ii) (), is reported. Their photophysical properties were studied by steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a large bathochromic shift of all the absorption bands, a notable increase in the absorption coefficient of the Q(0,0) band, and higher fluorescence quantum yield compared to porphyrin , with two unsubstituted meso positions. Cyclic voltammetry and digital simulation show that electrogenerated radical ions of are more stable than those of . The lack of substituents at the meso positions of leads to dimerization reactions of the radical cation. Despite this, the annihilation reaction of and produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical experiments demonstrate that the electroreduction of leads to a strong absorption band that might quench the ECL.

Phytotoxic Potential of Secondary Metabolites and Semisynthetic Compounds from Endophytic Fungus Xylaria feejeensis Strain SM3e-1b Isolated from Sapium macrocarpum.

Bioactivity-directed fractionation of the combined culture medium and mycelium extract of the endophytic fungus Xylaria feejeensis strain SM3e-1b, isolated from Sapium macrocarpum, led to the isolation of three known natural products: (4S,5S,6S)-4-hydroxy-3-methoxy-5-methyl-5,6-epoxycyclohex-2-enone or coriloxine, 1; 2-hydroxy-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione, 2; and 2,6-dihydroxy-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione or fumiquinone B, 3. This is the first report of compound 3 being isolated from this species. Additionally, four new derivatives of coriloxine were prepared: (4R,5S,6R)-6-chloro-4,5-dihydroxy-3-methoxy-5-methylcyclohex-2-enone, 4; 6-hydroxy-5-methyl-3-(methylamino)cyclohexa-2,5- diene-1,4-dione, 5; (4R,5R,6R)-4,5-dihydroxy-3-methoxy-5-methyl-6-(phenylamino)cyclohex-2-enone, 6; and 2-((4-butylphenyl)amino)-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione, 7. X-ray analysis allowed us to unambiguously determine the structures and absolute configuration of semisynthetic derivatives 4, 5, and 6. The phytotoxic activity of the three isolated natural products and the coriloxine derivatives is reported. Germination of the seed, root growth, and oxygen uptake of the seedlings of Trifolium pratense, Medicago sativa, Panicum miliaceum, and Amaranthus hypochondriacus were significantly inhibited by all of the tested compounds. In general, they were more effective inhibiting root elongation than suppressing the germination and seedling oxygen uptake processes as shown by their IC50 values.

Cambios en la percepción de la violencia y el comportamiento agresivo entre niños a partir de un programa de habilidades socioemocionales / Changes in the perception of violence and aggressive behavior among children based on a program of social and emotional skills

El objetivo de este trabajo fue medir el cambio en la frecuencia de victimización, comportamiento agresivo y comportamiento positivo de los niños, después de participar en el programa "Comunidades amigas de la infancia". Participaron 302 niños de entre 9 y 15 años, de quinto y sexto de primaria en dos escuelas públicas alta marginalidad en Guadalajara (México), que fueron evaluados con las escalas de victimización, agresión y conductas positivas de Orpinas (2009). Se observaron cambios en la percepción de la violencia de la cual son objeto los menores y un aumento en el reconocimiento de la agresión que ejercen hacia los compañeros en niños que inicialmente informaron no ser agresivos o que obtuvieron una puntuación baja en los niveles de agresión. Asimismo, aquellos niños que tienden a ser agresores mostraron una disminución significativa en la agresión, tanto directa como relacional, ejercida hacia sus iguales. Estos resultados sugieren que el programa "Comunidades amigas de la infancia" ayuda a disminuir la normalización de la violencia hacia los niños, así como los comportamientos agresivos hacia los compañeros

The aim of this research was to examine changes in the frequency of victimization, aggressive behavior and positive behavior among children after participating in the program "Child Friendly Communities". 302 children between 9 and 15 years of age participated; the children, who at the time of the intervention were completing the fifth and sixth grades of basic education in two public schools with high levels of marginalization, in the metropolitan area of Guadalajara (Mexico), were evaluated using Orpinas' (2009) scales of victimization, aggression and positive behaviors. We observed changes in their perception of the violence performed against them and a growing recognition of the aggression exercised by them against peers in those children who prior to the intervention reported not being aggressive or who obtained a low score on levels of aggression. Likewise, children who tend to be aggressors showed a significant decrease in aggression exerted against others, both direct and relational. Results suggest that the program Child Friendly Communities helps to decrease the normalization of violence against children as well as the aggressive behavior against peers

Preventing childhood anxiety and depression: Testing the effectiveness of a schoolbased program in Mexico

A growing number of school-aged children experience or are at risk for a myriad of psychological and behavioral problems such as anxiety and depression that interfere with their interpersonal relationships, school performance, and potential to become productive citizens –hence the importance of school prevention. This study assessed the effectiveness of the Spanish version of the FRIENDS for Life program [AMISTAD para siempre], a social and emotional program that uses cognitive-behavioral techniques to prevent anxiety and depression. Eight schools from a northern city in Mexico were randomly selected and assigned to either an intervention or standard curriculum instruction. Fifteen teachers implemented the intervention, and 16 served as control. Participants were 1,030 fourth and fifth grade students (ages 8-13). The impact of the program was evaluated immediately after the intervention and after 6 months. The program showed a positive effect by reducing symptoms and risk for depression and increasing the proactive coping skills of the overall sample. Suggestions for further research and implications for practice are offered (AU)

Un número elevado de niños de edad escolar experimentan o corren el riesgo de experimentar una serie de problemas psicológicos y de comportamiento tales como la ansiedad y la depresión, las cuales interfieren en sus relaciones interpersonales, el desempeño académico y el potencial para convertirse en personas productivas. El presente estudio evalúa la eficacia de la versión en español del programa FRIENDS for Life [AMISTAD para siempre], que enseña habilidades sociales y emocionales utilizando técnicas cognitivas-conductuales para prevenir ansiedad y depresión. Ocho escuelas de una ciudad al norte de México fueron aleatoriamente seleccionadas y asignadas a un grupo de intervención o al grupo de currículo estándar. Quince educadoras implementaron el programa y 16 maestras siguieron con el currículo estándar. Los participantes fueron 1.030 niños, de 8 a 13 años de edad, de cuarto y quinto grado de primaria. El impacto del programa se evaluó inmediatamente después de la intervención, y a los seis meses. Los resultados muestran que el programa tuvo efectos positivos al reducir los síntomas y el riesgo de depresión e incrementar las estrategias de afrontamiento proactivas de aquellos que lo recibieron. Se ofrecen sugerencias sobre futuras investigaciones así como sobre sus implicaciones para la práctica (AU)

Mechanism of the OH radical scavenging activity of nordihydroguaiaretic acid: a combined theoretical and experimental study.

The antioxidant nordihydroguaiaretic acid (NDGA) is a plant phenolic lignan originally isolated from the creosote bush (Larrea tridentata). It has been shown that NDGA scavenges efficiently hydroxyl radicals ((*)OH). In the present paper the mechanism by which NDGA scavenges (*)OH is addressed performing a combined experimental and theoretical investigation. We found that NDGA protects, in a concentration-dependent way, bovine serum albumin and DNA from the damage induced by (*)OH generated by the Fenton reaction. In addition, the NDGA + (*)OH reaction is predicted to be diffusion-controlled. The first step of this reaction is proposed to occur mainly by a sequential electron proton transfer from NDGA to (*)OH generating a neutral radical of NDGA, which after a second oxidation step gives a diradical that after a cascade sequential complex reaction produces a cyclic compound. This cyclic product is predicted to have a UV-vis spectrum very similar to that of NDGA, making its identification by this technique very difficult. The electrochemical studies performed in water support the formation of a cyclic compound (C2) as the main product of the reaction. It is concluded that NDGA can scavenge at least two (*)OH.

Electrochemical and chemical oxidation of dithia-, diselena-, ditellura-, selenathia-, and tellurathiamesocycles and stability of the oxidized species.

The diverse electrochemical and chemical oxidations of dichalcogena-mesocycles are analyzed, broadening our understanding of the chemistry of the corresponding radical cations and dications. 1,5-Diselenocane and 1,5-ditellurocane undergo reversible two-electron oxidation with inverted potentials analogous to 1,5-dithiocane. On the other hand, 1,5-selenathiocane and 1,5-tellurathiocane undergo one-electron oxidative dimerization. The X-ray crystal structures of the Se-Se dimer of the 1,5-selenathiocane one-electron oxidized product and the monomeric two-electron oxidized product (dication) of 1,5-tellurathiocane are reported. 1,5-Dithiocanes and 1,5-diselenocanes with group 14 atoms as ring members undergo irreversible oxidation, unlike the reversible two-electron oxidation of the corresponding silicon-containing 1,5-ditellurocanes. These results demonstrate the chemical consequences of the dication stabilities Te(+)-Te(+) > Se(+)-Se(+) > S(+)-S(+), as well as Se(+)-Se(+) > Se(+)-S(+) and Te(+)-Te(+) > Te(+)-S(+).

Electron transfer and structural change: distinguishing concerted and two-step processes.

In electron-transfer reactions accompanied by structural changes, the structural change can be concerted with electron transfer or can occur in a separate reaction either preceding or following the electron-transfer step. In this paper we discuss ways of distinguishing concerted reactions from the latter two-step type. Included are recent examples in which no intermediates have been detected in the reactions, thus precluding the direct assignment to the two-step category. In these cases, other means are used to build support for the two-step mechanism with respect to the concerted process. These include an example of structural change preceding electron transfer, a demonstration that the current models of concerted reactions cannot fit the voltammetric data, and a case in which an independent measure of the inner reorganization energy was used to show that the reaction could not be a concerted electron transfer and structural change.

Quantitative evaluation of the mechanism of electroreduction of benzoyl cyanides.

The mechanism of reduction of benzoyl cyanide, 6, p-methoxybenzoyl cyanide, 7, and p-chlorobenzoyl cyanide, 8, has been studied in acetonitrile (6 and 7), N,N-dimethylformamide (6), and acetonitrile containing water (all three compounds). The reaction proceeds by initial reduction to form the anion radical followed by dimerization to produce an intermediate dianion, the dianion of the dicyanohydrin of benzil. The latter loses cyanide to give the anion of the monocyanohydrin of benzil, which undergoes two parallel reactions: expulsion of cyanide to give the corresponding benzil and rearrangement to the monoanion of mandelonitrile benzoate. The addition of water brings about an increase in the dimerization rate constant and an associated increase in the amount of benzil that is produced. The standard potentials for the initial reduction step have been evaluated, and their dependence on the substituent is discussed. The dimerization rate constants have also been evaluated.

Electron-transfer reactions with significant changes in structure. Unsymmetrical crowded ethylenes.

The electrochemical reduction mechanisms of xanthylideneanthrone, 6, thioxanthylideneanthrone, 7, 10-(diphenylmethylene)anthrone, 8, and 9-(diphenylmethylene)-9H-fluorene, 9, have been studied in dimethylformamide. The reduction of the first two compounds proceeds from folded forms of the neutral to twisted forms of the anion radical according to a square scheme. The data for reduction of 8 can be well accounted for by the same square scheme. However, one-step reduction with concerted electron transfer and structural change cannot be ruled out. Compound 9, whose fluorene ring system cannot fold, exists only in twisted forms in the neutral, anion radical, and dianion. Consequently, there are no major changes in structure upon reduction, and the compound is reduced in two reversible steps with the second complicated by rapid loss of the dianion that is probably due to protonation by components of the medium.

Studies of potential inversion in an extended tetrathiafulvalene.

Electrochemical oxidation of the extended tetrathiafulvalene 9,10-bis(1,3-dithiole-2-ylidene)-9,10-dihydroanthracene (2) was studied in N,N-dimethylformamide. A single, two-electron oxidation peak occurs, and on the return sweep of a cyclic voltammogram, a two-electron reduction peak is seen. The oxidation of 2 to its cation radical and dication occurs with potential inversion (i.e., removal of the second electron occurs more easily than removal of the first). The extent of potential inversion was estimated by cyclic voltammetry to be 0.28 V by analysis of the process in terms of concerted structural change and electron transfer. Failure to detect the cation radical by EPR of an equimolar mixture of neutral 2 and the dication is consistent with this value. The inner reorganization energy of the cation radical was determined by gas-phase photoelectron spectroscopy (PES) to be 0.31-0.35 eV. Calculations, consistent with earlier experimental data, show rather large changes in structure associated with the oxidation processes. These large structural changes contrast with the relatively small inner reorganization energy found by PES. This observation prompted an analysis of voltammetry in terms of two-step processes, with structural change either preceding or following electron transfer. Agreement of simulations based on this mechanism with experimental voltammograms was equally as good as with the concerted mechanism. Notably, the two-step mechanism produced more realistic values of the transfer coefficient and electron-transfer rate constant for the first step of oxidation.

Change in reaction pathway in the reduction of 3,5-di-tert-butyl-1,2-benzoquinone with increasing concentrations of 2,2,2-trifluoroethanol.

The electrochemical reduction of 3,5-di-tert-butyl-1,2-benzoquinone, 1, has been studied in acetonitrile with added 2,2,2-trifluoroethanol, 2. At low concentrations of 2 the reaction proceeds by the following pathway: reduction of the quinone (Q) to its anion radical (Q*-) followed by complexation of the anion radical with 2 (HA) and the further reduction of the hydrogen-bonded complex (Q*- (HA)) to form HQ- and A-. The latter reaction is a concerted proton and electron- transfer reaction (CPET). At higher concentrations of 2, the pathway changes. The first steps remain the same, but now Q*- (HA) is reduced to HQ- via a disproportionation reaction with Q*- along with proton transfer from HA to Q*- to form HQ* which is reduced to HQ-. The only mechanism that could be found which would account for all of the data involves proton transfer to Q*- occurring within a higher complex, Q*-(HA)3.

Reduction of diesters of 1,2-diols. Regioselective C-O bond cleavage of the anionic forms.

The electrochemical reduction of benzoate diesters of glycols has been studied in acetonitrile and N,N-dimethylformamide as solvents. The reductions occur in two closely spaced one-electron steps, and it was found that the dianion diradicals decompose by one of two routes, depending on the substituents on the ethylene moiety: cleavage of two benzoates to produce alkene or formation of benzil by way of a postulated cyclic intermediate to produce also the dianion of the diol. These correspond to cleavage of the R-OC(O)Ar bonds and the RO-C(O)Ar bonds, respectively. When the radical formed by the former cleavage is a primary or secondary radical, the reaction is too slow to compete with the latter reaction that produces benzil. However, when that radical is either tertiary or benzylic, the former cleavage reaction is fast and no benzil is detected. The dianions of p-cyano- and p-nitrobenzoate esters are rather stable on the voltammetric time scale. However, the addition of lithium ions results in detectable formation of 4,4'-dicyanobenzil from four different p-cyanobenzoate diesters.

Reaction of thianthrene and phenoxathiin cation radicals with 2,3-dimethyl-2-butene. Chemical and electrochemical studies.

Thianthrene cation radical tetrafluoroborate (Th*+ BF4-) has been found to add to 2,3-dimethyl-2-butene (DMB) at 0 degrees C and -15 degrees C. The adduct, 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate (12), was isolated at -15 degrees C, and its 1H NMR spectrum was recorded at that temperature. The adduct was stable in CD3CN solution at -15 degrees C but decomposed slowly at 0 degrees C and quickly at 23 degrees C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline (8) with loss of thianthrene (Th). These results explain why earlier attempts to prepare 12 and detect its formation at room temperature with NMR spectroscopy were not successful. Reaction of Th*+ with DMB was followed with cyclic voltammetry and was found to exhibit redox catalysis in which Th was regenerated. With the faster scanning techniques of cyclic voltammetry, the formation of 12 was detectable, with a reduction potential of about -1.0 V at 25 degrees C and 3 degrees C. The observed reduction potential was in harmony with reduction potentials of a number of other, stable monoadducts. Thus, the redox catalysis involved the rapid formation of 12 and its rapid decomposition into 8 and Th, the newly formed Th being responsible for the observed enhanced oxidation currents. In contrast, 8 appears to be formed directly by oxidation of DMB by PO*+PF6-.

Studies of the inner reorganization energies of the cation radicals of 1,4-bis(dimethylamino)benzene, 9,10-bis(dimethylamino)anthracene, and 3,6-bis(dimethylamino)durene by photoelectron spectroscopy and reinterpretation of the mechanism of the electrochemical oxidation of the parent diamines.

The inner reorganization energy of the cation radical of 1,4-bis(dimethylamino)benzene, 1, has been determined to be 0.72 +/- 0.02 eV by means of gas-phase photoelectron spectroscopy (PES). PES studies of 9,10-bis(dimethylamino)anthracene, 2, and 3,6-bis(dimethylamino)durene, 3, demonstrate that their reorganization energies are smaller than that of 1. The effect of lowering the inner reorganization energy on the rate constant for an electrochemical electron-transfer reaction is to increase the electron-transfer rate constant, k(s). However, voltammetric studies of the two-electron oxidation of 2 and 3 indicate that the values of k(s) for each step are smaller than those for 1, in contradistinction to the measured differences in reorganization energies. The voltammetric studies of 2 and 3 were reinterpreted according to a mechanism in which each step of oxidation was written as a two-step process, electron transfer with a small inner reorganization energy plus a chemical step of structural change. The agreement of simulations according to this mechanism with the experimental data was excellent. The new reaction scheme eliminated some suspicious features previously obtained with an analysis where electron transfer and structural change were considered to be concerted. In particular, all electron-transfer coefficients (alpha) were close to one-half, whereas the earlier treatment produced values of alpha much larger or smaller than one-half.